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ASPHALT CONSTRUCTION 

FOR 

PAVEMENTS AND HIGHWAYS 



McGraw-Hill Dookfompaiy 

Electrical World TheEngineei-ing andMiiung Journal 
En^eoring Record Engineering News 

Railway Age Gazette American Machinist 

Signal LngirLQGr AmericatiEngpeer 

Electric Railway Journal Coal Age 

Metallurgical and Chemical Engineering Power 

g liM I MIIIllll l llil II II IIM I Il l l l ll ■■ II IIM^^ ^ ^^ ■■■ ■Illi^ 



1 



ASPHALT CONSTRUCTION 

FOR 

PAVEMENTS AND HIGHWAYS 

A POCKETBOOK FOR ENGINEERS 
CONTRACTORS AND INSPECTORS 



BY 

CLIFFORD RICHARDSON 

CONSULTING ENGINEER, MEMBER AMERICAN SOCIETY 
CIVIL ENGINEERS, FELLOW CHEMICAL SOCIETY 



McGRAW-HILL BOOK COMPANY 

239 WEST 39TH STREET, NEW YORK 

6 BOUVERIE STREET, LONDON, E. C. 

1913 



<^ 






Copyright, 1913, by the 
McGraw-Hill Book Company 



B-27Si 



THE.MAPL^PRESS.TORK.PA 

©CI.AoMVClO 



\ 
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4 PREFACE 

^) The increase in recent years in the amount of sheet 
asphalt pavement which is being laid in our cities and 
the extent of the asphaltic concrete and asphaltic broken 
stone surfaces which are being constructed on our country 
highways to resist the destructive action of motor ve- 
hicles, has created a demand for highway engineers, con- 
tractors, and inspectors, who are skilled in this work, far 
in excess of the supply. The result has been that many 
have entered these fields who do not realize the im- 
portance of careful attention to details which is necessary 
to insure complete success in this line of work. With a 
view to supplying the necessary information in regard 
to these details to the persons who have been mentioned, 
this pocket-book has, been prepared with the hope that 
it will do something toward insuring better^work in the 
future than has been done in some cases during recent 
years by inexperienced contractors and engineers, and 
supervised by inexperienced inspectors. Its form has 
been selected in order that it may be readily carried in 
the coat pocket, for reference on all occasions, something 
that cannot well be done with a larger book with stiff 
covers. 

The Author. 

April, 1913. 



CONTENTS 

Page 
Preface v 

CHAPTER I 

Introductory i 

CHAPTER II 
Broken Stone 5 

CHAPTER III 
Foundation 8 

CHAPTER IV 

The Intermediate Course 16 

Sheet asphalt pavements — Open binder — Close binder 
— Asphaltic concrete as a wearing surface — Asphaltic 
broken stone and asphaltic concrete country highways. 

CHAPTER V 

The Mineral Aggregate 25 

Sheet asphalt surfaces — Sand — Aggregate containing fine 
stone. 

CHAPTER VI 

Filler or Dust 35 

CHAPTER VII 

Native Bitumens 39 

Physical properties — Chemical characteristics — Trinidad 
lake asphalt — Refined Trinidad asphalt — Bermudez 
asphalt. 

vii 



viil CONTENTS 

CHAPTER VIII 

Page 

Fluxes 48 

CHAPTER IX 
Asphalt Cement 52 

CHAPTER X 

Surface Mixtures 56 

Sheet asphalt mixture — Laboratory rules and instructions 
for plant foremen and chemists — General information 
for plant chemists and foremen — Grit mixtures — Asphal- 
tic concrete surfaces — Asphaltic broken stone surfaces or 
asphalt macadam — Asphalt surface or carpet coats. 

CHAPTER XI 

Maintenance and Repairs 107 

CHAPTER XII 
The Plant 112 

CHAPTER XIII 
Work UPON THE Street 117 

CHAPTER XIV 

Advice to Engineers, Contractors and Inspectors . . . 121 
Suggestions to engineers — Suggestions to contractors — 
Suggestions to inspectors — Suggestions to citizens. 

CHAPTER XV 

Laboratory 127 

CHAPTER XVI 

Methods for Examination of Bituminous Materials 

AND Mineral Aggregates 130 

Mesh composition of mineral aggregate — Material finer 



CONTENTS IX 

Page 
than that passing 200 mesh in a filler — Total bitumen in 
refined asphalt and asphalt cement — Mineral matter or ash 
— Consistency or penetration of asphalt cements — Flow 
test — Examination of sheet asphalt surface mixtures. 

CHAPTER XVII 

Instructions for Taking Samples and Specimens of 

Materials for Exaivhnation 141 

Samples and specimens — Sand — Sampling sand — Dust 
— and filler — Fluxes — Asphalt cement — Surface mixtures 
— Sampling surface mixture. 

Index 151 



ASPHALT CONSTRUCTION 
FOR PAVEMENTS AND HIGHWAYS 

CHAPTER I 
INTRODUCTORY 

The design and construction of a sheet asphalt pave- 
ment involve three considerations,' the foundation, the 
intermediate or binder course, and the surface or wear- 
ing course. The same elements must be considered, 
although sometimes in a rather dififerent way, in the 
construction of an asphaltic road surface of broken 
stone or of a graded mineral aggregate. 

The municipal or highway engineer will provide a 
specification under which the construction work will 
be done by the contractor. This will be based, generally, 
upon past experience and on the results of successful 
service tests. In drafting such a specification the engi- 
neer should not be guided blindly by so-called standard 
specifications which are only of general application, 
nor should he, unless a person of very wide experience, 
depart too widely from them. Each specification 
should ^be so drawn as to apply to the individual case, 
to the particular environment where the work is to be 
constructed, and to the traffic to be met. It is useless 
to specify something which will call for the most perfect 
and most expensive form of construction where a cheaper 

1 



2 ASPHALT CONSTRUCTION 

one will prove satisfactory, and it is equally so to provide 
for a cheap form of construction where the highest 
type is necessary, and eventually will prove the most 
economical. A pavement which may originally cost 
$2.25 per square yard may eventually prove more 
economical than one costing but $1.75 per square yard 
if the former wears fifteen years and the latter but ten, 
aside from the increased cost of maintenance of the 
cheaper form of surface. This consideration applies 
equally well to highway construction and to sheet 
asphalt pavements. Economy in first cost, therefore, 
is no indication of the eventual saving of money, either 
to the municipality, the state, or the contractor. For 
the same reason both engineers and contractors should 
give careful attention in the first instance, to the charac- 
ter of all materials which are available for use in the 
construction of a street or road surface, not only from a 
financial point of view, but with due regard to the 
reputation of the individual for doing good work. Even- 
tual success, both structural and financial, will depend 
upon careful consideration of these matters. 

The contractor should be possessed of sufficient 
information, experience and intelligence to interpret 
the specifications under which he proposes to work, 
and of good judgment to carry them out in a way to 
redound to his profit and reputation. The longer 
that the paving or road contractor has been in the 
business, the more he will appreciate the benefit and 
necessity of selecting the best materials, those which 
have been proved by experience to give the best results, 
and of organizing a force which will work with such care, 
based upon knowledge and experience, as will yield 
the best results. Of course, the contractor can use 



INTRODUCTORY 3 

only the specific materials which are called for, and 
naturally he must use the cheapest form of each which 
is permitted; but where there is any choice and financial 
considerations allow, he will never go wrong in choosing 
the best which are available, and of a kind which extended 
experience and service tests have proved to be the 
most satisfactory, at least, if he intends to establish a 
high reputation and remain in business successfully 
for many years. 

The instructions to be given in the following pages 
will be based on these premises. They have been derived 
from observations and from the experience of the writer 
extending over thirty-five years, beginning in 1878 with 
the original Trinidad sheet asphalt surface laid on 
Pennsylvania Avenue in Washington, D. C, in 1876 
and the extraordinary surface laid in 1879 on Vermont 
Avenue in that city, which is still in existence to-day. 
To him this fact is convincing evidence of the lasting 
qualities of natural asphalt when satisfactorily manipu- 
lated, either by chance, or, as is now the case, by rational 
methods. 

Until 1894 sheet asphalt pavements were laid on 
empirical lines without any definite recognition of what 
sand grading was necessary for success, why finely 
ground mineral matter was added to the surface mixture 
or of the relations of asphalt cement to the combination 
of sand and dust, which is known as the mineral aggre- 
gate. A vast area of sheet asphalt surface had been 
constructed in cities where the travel at that time was 
not excessive, and where the greatest demands for 
stability were not made upon a surface of this type. 

In 1894 the writer was engaged to supervise the intro- 
duction of the sheet asphalt pavement of the American 



4 ASPHALT CONSTRUCTION 

type in London, England. It was found that it was 
impossible to construct one in that city, where the traffic 
was heavy and the surface moist for months at a time 
during the winter, which would meet these conditions 
satisfactorily by following the methods which had previ- 
ously been in use in the United States. A careful 
study of the subject was plainly necessary and was 
undertaken with a view of determining what were the es- 
sential principles which must necessarily be followed to 
produce a sheet asphalt surface that would resist the 
most trying conditions. The problem was solved in the 
next two years in a way which permitted the construction 
of pavements, subjected to heavy travel and continued 
moisture as in London, which have met every demand 
imposed upon them. In fact, the pavement so laid on 
Fifth Avenue, New York, proved satisfactory after 
fifteen years of use. 

It is proposed in this handbook to give in detail a 
statement of the procedure which must be followed in 
order to duplicate such construction at the present time, 
in a form which will make it available to the engineer 
and to the contractor who have not had the widest ex- 
perience in this direction in the past, and which will 
enable them to control the use of standard materials in 
such a way that they may not be discredited, as it must 
be recognized that in unskillful hands the best materials 
may prove unsatisfactory. 



CHAPTER II 
BROKEN STONE 

Broken stone is an important element in the con- 
struction of a concrete foundation for all pavements, 
of the binder or intermediate course of sheet asphalt 
pavements, as a component of asphaltic concrete, and 
in asphaltic broken-stone surfaces for country highways. 

Stone for any of these purposes should be derived 
from a hard rock, preferably a trap or hard, not coarsely 
crystalline, limestone. It should yield fragments, on 
being crushed, of satisfactory shape and fracture. The 
fragments should not be of a spally nature, that is to 
say, not thin and flat, but should be as nearly as possi- 
ble cubical. Rocks of various origin behave differently 
in crushers, and in consequence the production of good 
broken stone is dependent upon very many conditions, 
connected not only with the stone which is the source 
of supply of this material, but upon the manner in which 
the crushing is done. As an illustration of the method 
by which crushed trap-rock has been made on the 
Hudson, the following details may be of interest. 

Stone from a No. 8 Gates crusher was passed over an 
initial screen 15 ft. long with 2 i/8-in. holes to produce 
I 1/2-in. stone, the pitch of the screen being i in. to the 
foot. The tailings, of course, went back to a smaller 
crusher No. 5 and the material from this crusher was 
passed over a secondary screen 20 ft. long, with 3 ft. of 
I 3/8-in. holes, and 11 ft. of i 1/4-in. holes for the pro- 

5 



6 ASPHALT CONSTRUCTION 

duction of 3/4-in. or binder stone. There were also 6 
ft. of 2 i/8-in. holes for i 1/2-in. stone. The screen 
was jacketed with a dust jacket 7 ft. long perforated 
with 5/8-in. holes to remove the stone and dust passing 
apertures of this size. The pitch of this screen was 
the same, i in. to the foot. With the demand for clean 
stone of 3/8-in. size for the surface of asphaltic broken- 
stone roads the dust was removed from material passing 
5/8-in. holes with an 8 mesh to the inch screen. 

With screens of this description broken stone is pro- 
duced for hydraulic concrete and for use in the wearing 
surface of asphaltic broken-stone roads. The 3/4-in. 
stone is suitable for use in binder, and for asphaltic con- 
crete. The use of the pea grit, 3/8-in. ^ize, has already 
been mentioned. The screenings or dust from this can be 
utilized for conversion into filler by grinding in suitable 
mills. 

For binder, trap-rock and limestone, if the latter is hard, 
are equally suitable, and the same is true of stone of pea- 
grit size used for grit mixtures. For asphaltic broken- 
stone surfaces the hard limestone is preferable to trap- 
rock, as asphalt adheres to the surface of fractured lime- 
stone better than to the glassy surface of trap-rock. 

In some cases the run of crusher, that is to say, broken 
stone consisting of all sizes, after the removal of the 
coarser material not passing the 2 i/8-in. holes and of the 
fine dust, has been used for the construction of asphaltic 
broken-stone roads and for asphaltic concrete. The 
difficulty with such material is that it segregates during 
transportation or handling at the plant, the smaller 
sizes separating from the larger, but with it successful 
asphaltic concrete has been prepared, with the addition 
of sand, when necessary. 



1 



BROKEN STONE 7 

Stone, other than trap-rock or hard limestone, should 
not be used for asphaltic surfaces with the expectation of 
obtaining the best results. A less satisfactory stone, a 
granite or field stone, may be used in the binder or inter- 
mediate course, without danger, owing to the protection 
which it will have from the surface coat. 



CHAPTER III 
FOUNDATION 

A city pavement or a country road surface is of little 
value unless it is adequately supported, and for this it 
must depend upon its foundation. The latter in reality 
carries the load which is imposed upon the pavement or 
road, while the surface merely serves as a means of trans- 
mitting it to the foundation. The extent to which a 
pavement or highway will prove durable will depend, 
therefore, on the adequacy of its foundation. It must 
be, further, remembered that the foundation itself is 
placed upon the soil, and supported by it. The soil, 
therefore, should either be adequate for this purpose in 
itself or should be made so by drainage or the removal of 
soft material. This necessity is taken up by the writer 
in greater detail in '^The Modern Asphalt Pavement," 
Chapter I. 

As the foundation is an essential feature, and one of the 
most important ones, in the construction of a durable 
pavement or highway surface, both the engineer in his 
specifications and the contractor in his construction work, 
should see that it is adequately provided for, and prop- 
erly constructed. The most satisfactory foundation for 
any form of highway surface, including both city streets, 
and country roads, is one of hydraulic concrete of suffi- 
cient thickness. In view of the increased weight and 
number of vehicles which are using our streets and the 

8 



FOUNDATION 9 

many roads which are main arteries of travel, the neces- 
sary thickness should be provided. 

It will be impossible to avoid the construction of such 
foundations in the future for important work, and this is 
the less to be regretted since, when properly built, they 
are durable and will last for many years, the surfaces 
which they sustain being renewed from time to time. 
They can be written up as capital and can be properly 
financed by long-term bond issues. 

The thickness of hydraulic concrete necessary will vary 
under different circumstances. It has usually been 6 
in. for sheet asphalt pavements carrying the heaviest 
traffic, which is at times reduced to 4 in. on residence 
streets. Such a thickness will not be found sufficient, 
according to the writer's idea, to carry the travel which 
is promised in the future, either on such streets or on some 
of our country highways. With the advent of the motor 
truck, the traction engine and the motor omnibus English 
engineers have arrived at the conclusion that not less 
than 9 in. of concrete will be required to furnish a satis- 
factory support. Such a thickness will be eventually 
demanded in the United States because in the area in- 
cluded in a radius of 30 miles or more about our own large 
cities motor trucking is becoming common, with loads 
amounting frequently to 10 tons. 

It is not necessary in this place to offer a treatise on 
modern methods of concrete construction. It is impor- 
tant, however, to call attention to the necessity of careful 
consideration of the character of the sand which is to be 
used. Sands which appear to be satisfactory are fre- 
quently not so, and their character can only be deter- 
mined by testing them with the Portland cement to be 
used in the work. No sand should be employed which 



10 ASPHALT CONSTRUCTION 

does not give a tensile strength, with the Portland cement 
selected, of at least 80 per cent, of that obtained with it 
with standard Ottawa sand. In the best practice it will 
also be found advisable to select that Portland cement 
among those which are available, which will give the best 
results with the local sand, as it has been found that 
cements differ largely in this respect, one brand in some 
cases working more successfully than another. This has 
been demonstrated on several occasions, especially where 
the work is done at low atmospheric temperatures. 
This is a matter, however, more for the regulation of the 
municipal or state engineer than for the contractor. It 
is not given, at the present time, as much consideration 
as it should be. With the cement, sand and broken 
stone selected for the concrete, attention must be given 
to the manner in which these are combined and placed 
upon the street. To-day the mixing is usually done by 
power mixers, which produce a more thorough mixture 
than is possible with hand labor and more economically. 
The condition which demands the most careful control, 
especially in some forms of mixers, is the regulation of 
the percentage of water which the mixed concrete con- 
tains; if it is too dry it will not ram or set well, but an 
excess of water will permit the ready segregation of the 
different-sized particles. A recent writer^ on concrete 
has stated the case very well, as follows : 

"When fine and coarse particles are suspended in a liquid 
the coarse, by virtue of their greater weight compared with 
their surface, tend to work toward the bottom, displacing the 
fine matter upward; for it must be remembered that a body 
falling through a liquid always generates an upward current 

^ Dr. J. S. Owens, The "Surveyor," Feb. 7, 1913. 



FOUNDATION 11 

to fill the space which it occupied, and this is sufficient to 
keep very fine particles suspended. The case of immediate 
interest is that of concrete mixed with too much water; in 
such, when kept in a state of disturbance by ramming, there 
is a tendency for the coarse part of the aggregate to work 
toward the bottom, the finer sand and cement toward the top 
giving a deceptive appearance to the concrete of having been 
thoroughly consolidated. '^ 

For the above reasons given by Dr. Owens, the 
concrete after having been placed on the street should 
not be rammed too long, especially if it is very wet. 

Instead of using broken stone as the coarse portion of 
the mineral aggregate of a hydraulic concrete, gravel, or 
a mixture of broken stone and gravel may be employed. 
Clean screened gravel alone makes excellent concrete 
if the components are properly proportioned. The voids 
in the gravel should be determined and the amount of 
Portland cement mortar necessary to slightly more than 
fill them calculated, but the gravel should not be used in 
any empirical proportions, such as 1:3:6; the propor- 
tions must be determined for each gravel, and will 
depend upon its grading. Where gravel which is the run 
of the bank is used, the amount of fine material which 
plays the rok of sand must be determined and allowed 
for, and satisfactory results are only obtained when due 
consideration is given to this and the mineral aggregate 
is properly proportioned. Mixtures of broken stone and 
gravel, where the size of the latter is suitable for filling 
the voids in the stone, make a very satisfactory concrete, 
as an example of which the foundation under the Fifth 
Avenue pavement in New York, which was laid in 1896-7, 
may serve. The presence of gravel in the voids in the 
broken stone reduces the volume of Portland cement 



12 ASPHALT CONSTRUCTION 

mortar which is necessary, and at the same time facili- 
tates the putting of the material in place by ramming. 

The manner in which the surface of a Portland cement 
concrete foundation for sheet asphalt pavements is fin- 
ished demands some consideration. It has usually been 
thought that this should be left in a rough condition, 
with fragments of stone projecting above the surface of 
the mortar, and this procedure has even gone so far as to 
imbed sharp fragments of stone in the mortar before it 
is set. In the writer's opinion, this is a serious mistake. 
There are good reasons why the surface should be made 
as smooth as possible, and even floated with mortar, as 
is done in Great Britain and on the Continent, namely, 
that where it is not smooth and where stone projects, the 
thickness of the bituminous courses, binder and surface, 
differs at different points. In compressing these courses 
the roller will ride over the lowest portions of the founda- 
tion and the compression at these points will be less than 
elsewhere. Under travel those portions of the pavement 
which have not received complete compression under the 
roller will be compressed by it to an additional extent, 
thus permitting the formation of surface depressions 
which may be the cause of subsequent displacement 
due to the impact of the wheels of vehicles. The 
irregularity and waviness of many bituminous pave- 
ments is, undoubtedly, to be attributed to such a cause. 
The writer, therefore, advocates a smooth finish with 
concrete foundation for any form of bituminous surface. 

Foundations other than concrete are frequently used 
for sheet asphalt pavements, and for bituminous road 
surfaces, very often in both instances, old, water-bound, 
broken-stone roads. Where such a surface is on firm 
soil and has been subjected to travel for many years, it 



FOUNDATION 13 

has frequently proved most satisfactory, as for example, 
on Broadway above 59th Street, New York City, where 
a sheet asphalt pavement has been satisfactorily main- 
tained for many years on an old broken stone surface, 
and is only now being slowly replaced as new surfaces 
are constructed. On country highways it has frequently 
been successful, although not always so, especially where 
there is lack of drainage. In constructing a bituminous 
broken-stone road in the country care should be taken 
that drainage is supplied at all points where there is any 
accumulation of water or a clay bottom, which is liable 
to be thrown out of place by frost. 

A striking example of the suitability of an old water- 
bound broken-stone road as a foundation for a bituminous 
pavement, is seen on the Victoria Embankment in 
London. This roadway in 1906 consisted of a great 
depth of water-bound broken stone accumulated during 
a long period of years, the thickness being due to the 
continued application of broken stone in attempts to 
maintain the surface. It had an extremely high crown 
or camber. With the advent of motor trafl&c on the 
Embankment, the surface w^as found to be entirely 
inadequate to meet the conditions imposed upon it, and 
trials were made of numerous forms of bituminous 
pavements to overcome the difficulty. Among these was 
a sheet asphalt surface placed upon 3 in. of asphaltic 
concrete upon the old broken stone, after it had been 
graded to the proper contour. This form of construction 
has now been in place, in certain portions, for seven 
years, and the foundation has proved to be entirely 
adequate to support the asphalt concrete binder and the 
surface placed thereon under the heavy travel which the 
roadway carries. 



14 ASPHALT CONSTRUCTION ' 

Old brick pavements which are worn and have a 
rough surface form an excellent foundation for sheet 
asphalt pavements, and the same may be said of Port- 
land cement concrete surfaces. On this account, where 
pavements of these types are constructed, they should 
originally be laid at such a grade, as to permit of the 
addition of a bituminous surface when the original one 
becomes unsatisfactory. 

In the early days of the sheet-asphalt paving industry 
a so-called bituminous foundation consisting of a coarse 
broken stone, bound to a certain extent with some form 
of bituminous material, was in use, but this has been 
entirely abandoned in good practice, as it possessed no 
rigidity, and for the same reason it should be abandoned 
on country highways. In addition it is very difficult 
to remove an old surface from such a foundation, and 
to replace it with a new one, owing to the adhesion of 
the one to the other. 

To-day in the construction of country highways the 
foundation, if it may be called such, is really an inter- 
mediate course, consisting of broken stone of a size 
larger than that in use in the wearing surface, the frag- 
ments being as much as 2 1/2 in. in diameter. This 
is in itself supported only by the sub-soil and, especially 
on poor soils, where the travel is heavy, it is a quite 
inadequate and eventually a very expensive form of 
construction, as much of the stone is lost by being com- 
pressed into the soil. Such a course, except on the most 
stable soil, frequently becomes of little value, being 
displaced under heavy travel. 

It is frequently provided that the lower course of 
broken stone shall be covered with a filler of fine material 
but, according to the writer's idea, this is a great mis- 



FOUNDATION 15 

take, since the fine particles act as a lubricator to 
facilitate the movement of the coarse broken stone and, 
when driven into the mass by travel or settlement force 
the stone apart and prevent the proper bearing of the 
fragments on one another, depriving the course in conse- 
quence of its greatest stability. Fine material, in addi- 
tion, possesses a capillary action and holds water, which 
is undesirable. A course of clean broken stone offers 
much better drainage. 

It cannot be too strongly reiterated here, that in the 
construction of any form of pavement or highway, 
provision should be made for the prompt removal of 
water from the foundation, and also from any possible 
action on the intermediate course or surface, as there is 
no greater enemy to durability in any form of highway 
construction, than water. 



CHAPTER IV 
THE INTERMEDIATE COURSE 

Sheet Asphalt Pavements. — In the early days of the 
construction of sheet asphalt pavements, no intermediate 
or binder course of stone was used between the founda- 
tion and the surface, but it was soon found that greater 
stability was obtained in the surface if it was provided 
for. In the thicker surfaces which were originally 
used there was great liability to displacement under 
travel, making the surface uneven, wavy and unpleasant 
to ride over. An intermediate or binder course was 
first introduced into the sheet asphalt pavement industry 
in Washington in 1888, for the reasons given and its use 
has, since that time, become general. For a period of 
nearly twenty years it consisted of a course of broken 
stone 3/4 to I in. in largest diameter, coated with bitu- 
minous material and compressed under a roller. Within 
the last ten years an asphaltic concrete, consisting of a 
mineral aggregate of properly proportioned broken stone 
and sand, with an asphalt cement as a cementing ma- 
terial, has, on the suggestion of the writer, replaced the 
simple broken-stone binder originally used. These two 
forms of intermediate course are known respectively as 
open and close binder. 

Open Binder. — Open binder consists of stones largely 
of one size, the fragments being from 3/4 to i in. in 
their largest diameter, although at times run of crusher 
has been used. Broken stone of the latter description 
requires a larger amount of bituminous cementing 

16 



THE INTERMEDIATE COURSE 17 

material, and in consequence the binder is more cohesive. 
The following data will show the average composition 
of open binders which have been used at different times 
in the construction of sheet asphalt pavements. 

It appears from these figures that the percentage of 
bitumen which a binder requires depends largely upon 
the amount of fine material which it contains. The 
first mentioned in the table contains 26.8 per cent, of 
fine material and requires 5.4 per cent, of bitumen, 
while those made from cleaner stone where the fine 
particles do not exceed 5 per cent., contain less than 4 
per cent, of bitumen. In preparing, sending to the street, 
and placing a course of open binder, care is demanded 
in certain directions. The stone should be hard, suf- 
ficiently so not to crush under the roller. It should be 
free from clay and dirt, although as has been said, fine 
particles of the stone itself are an advantage rather than 
otherwise. In heating the stone and mixing it with 
the asphalt cement, great care should be used that it 
is not overheated, since if this is the case a proper coat- 
ing of the bonding material will not adhere to the stone, 
owing to the excessive heat, or much of it may run off 
and be lost during the haul to the street. On the other 
hand, the binder should be hot enough to permit of 
properly coating it and its ready compression on the 
foundation. An open binder should be bright and glossy, 
and not dead in appearance, as it is dumped from the 
truck. It should be hot enough to spread readily and 
uniformly. It should contain no excess of bitumen 
at any one spot, and should this be the case, such spots 
should be remoyed and replaced. Binder after it has 
been placed on the street or road, should be covered 
within the shortest space of time possible with the sur- 



18 



ASPHALT CONSTRUCTION 









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lO IJO K 


lO CO M 


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THE INTERMEDIATE COURSE 19 

face, as when it has been wet, tracked with dirt, or 
become covered with horse-droppings or dead leaves, the 
adhesion of the surface mixture to it will not be complete. 
In actual practice a 9 cu. ft. box of broken stone for 
binder which will weigh about 900 lbs. will require 
about 40 lb. of Trinidad and about 36 lb. of Bermudez 
asphalt cement, but the cement must be regulated by 
observing the appearance of the material in the truck 
and on the street. 

In preparing a binder at the plant the mixer in use 
should have teeth with a sufficient clearance between 
them and the lining of the mixer so that the largest 
particles of stone cannot become wedged between them, 
and thus rapidly wear out the lining of the mixer. It 
is not good practice to attempt to mix binder in the 
same mixer that is employed for preparing the surface 
mixture. A separate one should be employed, although in 
some of the smaller plants of a portable description, it is 
not always possible to do so, in which case provision must 
be made for making a change of teeth from the longer to 
a shorter form, in changing from surface to binder mixing. 
Close Binder. — -Close binder is, or should be, a true 
asphaltic concrete. It consists of the same broken stone 
of which the open binder is made, but the voids in it are 
filled with smaller stone and with an asphaltic mortar 
corresponding to the ordinary asphalt surface mixture. 
For the construction of a close binder or asphaltic 
concrete of the highest type, the grading of the mineral 
j aggregate should be carefully regulated. This can be 
I done by determining the voids in the coarser stone, 
calculating the amount of fine stone necessary to fill 
I these, and again the amount of sand to fill those in the 
mixture of coarse and fine stone. This can be readily 



20 



ASPHALT CONSTRUCTION 



done by constructing a box of sheet-iron or wood of 
exactly i cu. ft. capacity. It is filled with the hot coarse 
stone which is compacted by shaking. The surface is 
then struck off and the box weighed. Allowing for tare, 
the weight of i cu. ft. of the coarse stone is obtained. 
Knowing the density of this stone, 2.65 for limestone 
and 2.9 to 3.0 for trap-rock, the weight of a solid cubic 
foot of the stone can be calculated. By dividing the 
weight of a cubic foot of the broken stone by the weight 
of a solid cubic foot of the material, the voids can be 
determined. In the same way the weight of a cubic 
foot of the finer stone and of the sand can be arrived at. 
One can readily calculate the amount of each which it is 
necessary to use to fill the voids in the coarse stone, and 
again in the mixture of the coarse and fine stone. The 
proportions for actual use can be readily determined and 
the amount of bitumen required from the percentages 
of broken stone and sand that are present. 

As an example of the proportions of coarse stone, fine 
stone, sand and asphalt cement in actual use in preparing 
a close binder, the following figures will serve: 



New York 



Plant I 



Plant 2 



Boston 



Coarse stone 

Fine stone 

Sand 

Trinidad asphalt 

cement. 
Bermudez asphalt 

cement. 



480 lb. = 54-6% 
200 lb. = 22. 7 
ISO lb. = 17.0 



480 lb. = 53.3% 
202 lb. = 22. 4 
150 lb. = 16.7 
68 1b.= 7.6 



88s lb. = 73.4^ 

2S0 lb. = 20.8 

70 lb.= S.8 



S0lb.= 5-7 



880 lb. = 100.0 



900 lb. = 100. o 



i,20S lb. = 100. o 



5.6% 


5.2% 


4.8% 


4-4 


6.4 


4.2 


29.2 33-6 


29.0 35.4 


26.4 


1.8 


2.0 


.8 


lO.O 


7.0 


4.4 


23.2 


25.8 


24.4 


13-6 


17.8 


32.2 


7-4 


6.8 


2.8 


4.8 


0.0 


0.0 



THE INTERMEDIATE COURSE 21 



Bitumen soluble in CS2 

Passing 200-mesli screen 

Passing I o-mesh screen 29.2 33.6 29.0 35.4 26.4 30.6 

Passing 8-mesh screen 

Passing 1/4-in. screen 

Passing 1/2-in. screen 

Passing 3/4-in. screen 

Passing i-in. screen 

Retained i-in. screen 



At some plants it is impossible to separate the stone 
into coarse and fine particles, in which case the heated 
stone of both sizes is collected in one bin, but segregation 
generally occurs under such circumstances. In arranging 
the grading of the mineral aggregate care should be taken 
to see that the amount of fine material, while sufficient 
to fill the voids in the stone, is not present in excess, 
since in this case the surface of the binder when com- 
pacted on the street will be too smooth to bond properly 
I with the wearing surface, and resulting displacement 
under travel will be possible. An excess of bitumen 
must also be avoided for the same reason, and if spots in 
the binder as laid show anything of this description, the 
material should be removed. 

An entirely satisfactory close binder^ can be con- 
structed for all but the most trying conditions by the 
use of selected old surface material, which has been dis- 
integrated and softened -by steam, for filling the voids 
I in the ordinary open binder. It is, of course, a matter 
of great economy to turn out a close binder in this 
manner. The old surface material having been crushed 
and softened by dry steam, is added in the mixer to the 
hot binder stone and, in this manner, further disinte- 



22 ASPHALT CONSTRUCTION 

grated and distributed among the stone. The proper 
amount of additional asphalt cement is added to coat 
the stone and enrich the old surface mixture. It does 
not possess the complete stability of an asphaltic con- 
crete but it is infinitely superior to the ordinary open 
binder for the construction of an intermediate course. 

The asphalt cement in use in binder may well be 
considerably softer, ten to fifteen points, when it is 
possible to make it so, than that in use in the sheet 
asphalt surface. 

In the construction of asphalt pavements with an 
asphaltic concrete binder course, the surface should be 
applied to it before it has become entirely cold. It is 
well to run out binder to the street for not more than 
half of a working day and to cover it with surface during 
the same day. This is much more important with a 
close than with an open binder. It is not possible to do 
satisfactory work where a large area of close binder is 
laid on one day and covered with surface on the next. 

Asphaltic Concrete as a Wearing Surface. — It is be- 
coming more frequent to construct the wearing surface of 
a pavement with asphaltic concrete. In that case there 
is, of course, no intermediate course. The grading of the 
mineral aggregate of an asphaltic concrete for surfaces 
is a more important matter than when it is used as a 
binder and protected by a sheet asphalt surface. It 
requires, in order that it may have the greatest dura- 
bility, the use of a certain amount of filler, that is to say, 
the finer portions of the concrete should be as carefully 
graded as an ordinary sheet asphalt mixture. 

In many cases, as in Washington D. C, successful 
surfaces for moderate travel have been laid by combining 
the ordinary sheet asphalt surface mixture with the open 



THE INTERMEDIATE COURSE 



23 



binder composed of run of crusher st one, which are so 
proportioned that the sheet asphalt mixture exactly or 
slightly more than fills the voids in the stone. Such a 
mixture, laid on 13th Street in that city in 1910, had the 
following characteristics: 



ASPHALTIC CONCRETE LAID ON 13TH STREET, WASHINGTON. 

D. C, 1910 



Test No 117,967 

Bitumen 7-8% 

Passing 200 mesh 2.7 



Passing 10 mesh 30-o J 



32.7 



117,968 

7-5% 
1.6 

■ 27.9 



26.3 



Passing 8 mesh 8 

Passing |-in. holes 3.8 



4.6 



.6 
3-0 



3-6 



Passing J-in. holes 14.0 

Passing |-in. holes 22.5 

Passing i-in. holes 11 .4 

Retained i-in. holes. ... 7.0 



Specific gravity, sand. . . 

Specific gravity, stone. . 

Specific gravity, mineral 
aggregate 

Voids in mineral aggre- 
gate 



54.9 



100. o 

2.65 
2.91 

2.8l( 



17- 



12.4 
17.0 

I7.4 

14.2 



61 .0 



100 


.0 


2 


6s 


2 


.91 


2 


826 


24 


.8% 



The above mixtures have proved very satisfactory 
under the environment to which they have been exposed. 
They are plainly deficient in filler and their lasting 
properties would be increased if more had been used. 



24 ASPHALT CONSTRUCTION 

Asphaltic Broken Stone and Asphaltic Concrete 
Country Highways. — These types of surfaces are seldom 
supported upon an intermediate course; unless the course 
of large broken stone on which the bituminous surface is 
placed in the case of asphaltic broken-stone roads, may 
be considered as such rather than as a foundation. 
Asphaltic concrete is usually placed directly upon an old 
macadam or upon a Portland cement concrete foundation. 
More will be said of these surfaces in subsequent pages. 



CHAPTER V 
THE MINERAL AGGREGATE 

Sheet Asphalt Surfaces. — Sheet asphalt surfaces are 
constructed to carry the travel upon the street or road 
and transmit the load or burden to the foundation. 
They are intended to withstand wear and tear and the 
action of the elements. They consist of a mineral 
aggregate of sand, at times some fine stone, filler of 
impalpably fine ground mineral matter and an asphalt 
cement. The whole may be looked upon as an asphalt 
mortar, or where broken stone is present to the extent 
of 50 per cent, or more, as an asphaltic concrete. 

The character of the mineral aggregate, since it forms 
at least 90 per cent, of the pavement, is one of the most 
important things to be considered, and the greatest 
care should be taken in choosing the material of which 
it is made up. In a sheet asphalt pavement of the 
ordinary type, sand forms at least 80 per cent, of the 
mineral aggregate, the remainder consisting of filler 
and asphalt cement. 

SAND 

In the early days of the asphalt paving industry the 

suitability of the sand for the purpose was given little 

attention, any sand locally available being used without 

particular regard to its grading, that is to say, the relative 

I proportion of grains of different sizes of which it is made 

I up. Too often a sand which would make a good cement 

i mortar was considered suitable for the purpose. In 

I 25 

I 



26 ASPHALT CONSTRUCTION 

the course of years it was demonstrated that some sheet 
asphalt pavements were infinitely superior to others in 
durability. With a view of determining to what this 
was to be attributed, specimens of surfaces which had 
withstood service tests well and poorly were collected 
by the writer as long ago as 1894 and the character of 
the mineral aggregate determined in the laboratory. In 
the case of two exceptional pavements, one laid on Ver- 
mont Avenue between " H " and '^ I '' Streets in Washing- 
ton, D. C, in 1879, which is still in existence and in satis- 
factory condition, and another of excellent character on 
Court Street in Boston, the surfaces were found to have 
been made with fine sand, while those surfaces which had 
behaved badly in different parts of the country consisted 
largely of coarse sand with a great deficiency in fine 
grains and filler. This made it evident that the character 
of the sand is a very important consideration, and that 
its grading must be carefully considered. The character 
of sand can be determined by separating it into particles 
of different sizes by means of sieves. The sieves which 
are conventionally used for this purpose consist of a 
series of screens of woven wire cloth of different sized 
wire and openings or meshes between the wires of 
200, 100, 80, 50, 40, 30, 20, and 10 meshes to the lineal 
inch. The size of the particles which these screens pass 
bear a numerical ratio to each other. Such sieves are 
now made with great care and are standardized by the 
U. S. Bureau of Standards at Washington. By their 
use the exact grading or character of any available 
supply can be determined. As an example the following 
data in regard to a very desirable sand in use in Phila- 
delphia and a very undesirable river sand from the 
Ohio River at Louisville, may be given. 



THE MINERAL AGGREGATE 



27 





Philadelphia 




1905 


1912 


Passing 200 mesh 

Passing 100 mesh 

Passing 80 mesh 


0% 

22 
18 

30 
14 
7 
5 
4 



1.9% 
12.6 

16.5 

35-3 
6.2 


Passing 50 mesh 


Passing 40 mesh 


Passing 30 mesh 

Passing 20 mesh 


12.5 
6.8 


Passing 10 mesh 

Retained 10 mesh 


8.2 
2.0 








100. 


100. 



Louisville — River 



200 mesh 
100 mesh 
80 mesh 
50 mesh 
40 mesh 
30 mesh 
20 mesh 
10 mesh 



2% 

4 
53 
25 
10 

3 
2I 

100% 



28 ASPHALT CONSTRUCTION 

The satisfactory Philadelphia sand, it will be observed, 
contains, in one year, 40 per cent, and in another 29 per 
cent, of grains of 100- and 80-mesh size. The unsatis- 
factory sand contains but 5 per cent, of such sized grains 
and, on this account, would be unsuited for use by it- 
self in constructing a durable sheet asphalt pavement. 
It is evident, therefore, that in preparing for the con- 
struction of a sheet asphalt pavement in any locality 
the first thing to determine is whether a satisfactory 
sand supply is available, and this can only be done by 
the collection of samples and their examination with the 
sieves which have been mentioned. It will appear, 
later on, in the consideration of the surface mixture as 
a whole, that in determining the characteristics of the 
sand the essential features are that it shall contain suf- 
ficient material of the size passing 100- and 80-mesh 
screens, not too large an amount of coarse grains passing 
sieves of 30, 20 and 10 meshes to the inch, that is to say, 
material retained on a 40-mesh screen, and a very small 
amount of material passing a 200-mesh screen. The 
last is found to be undesirable and does not contribute 
stability to the surface mixture, unless it is entirely of 
the nature of a filler, in which case much of it will be 
blown away on passing through the sand drums on 
heating. For this reason, for ordinary purposes, a sand 
may be examined more simply with three sieves, de- 
termining the amount passing a 200-mesh screen, that 
passing an 80 but retained on a 200-mesh and the amount 
remaining on a 40-mesh screen. 

As a result of extended experience a sand which will be 
satisfactory for the construction of the most durable type 
of sheet asphalt pavement, to withstand heavy travel, 
should average as nearly as possible to the grading given 



THE MINERAL AGGREGATE 



29 



below. For less important work and lighter travel 
sands containing a smaller amount of fine material may 
be used, and the grading of such a possible material is 
also given. 



Heavy Traffic 



Light Traffic 



200 mesh 
100 mesh 
80 mesh 
50 mesh 
40 mesh 
30 mesh 
20 mesh 
10 mesh 



17-0% 
17.0 
30.0 
13.0 
10. o 
8.0 

5-Q 

lOO.O 



34-0 



23.0 



26.0% 

30.0 
13.0 

r 30 o 



It sometimes 'occurs that no single local supply fur- 
nishes a sand which will correspond to this grading. In 
such a case it may be necessary to combine two or three 
sands to accomplish the desired result, or it may prove 
cheaper to do this than to use a single expensive source 
of supply. As an example of this may be cited the 
necessity for mixing two sands in arranging the mineral 
aggregate for the sheet asphalt surface laid on Fifth 
Avenue in New York in 1896-97. The local supply of 
sand sifted as follows: 



30 ASPHALT CONSTRUCTION 

Passing 200 mesh 2 per cent. 

100 mesh 6 per cent. 

80 mesh 9 per cent. 

50 mesh 25 per cent. 

40 mesh 26 per cent. 

30 mesh 14 per cent. 

20 mesh 10 per cent. 

10 mesh 8 per cent. 

100 per cent. 

This contained but a total of 17 per cent, of material 
passing the 200-, 100-, and 80-mesh screens, which is a 
decided deficiency. It was, therefore, mixed with a 
finer sand coming as ballast from South Africa, which 
sifted as follows: 



Passing 200 mesh 6 per cent. 

100 mesh 13 per cent. 

80 mesh 29 per cent. 

50 mesh 35 per cent. 

40 mesh 9 per cent. 

30 mesh 5 per cent. 

20 mesh 2 per cent. 

10 mesh I per cent. 

100 per cent. 

The combination of the two in the proportion of 2/3 
coarse to 1/3 fine sand resulted in a more satisfactory 
grading, as will be seen by calculating the result. The 
mixture would be as follows: 



THE MINERAL AGGREGATE 31 

Passing 200 mesh 3 per cent. 

100 mesh 8 per cent. 

80 mesh 16 per cent. 

50 mesh 29 per cent. 

40 mesh 20 per cent. 

30 mesh II per cent. 

20 mesh 7 per cent. 

10 mesh 6 per cent. 

100 per cent. 

The resulting surface mixture made with the sand 
when combined with filler and asphalt cement will be 
discussed in another chapter. 

The necessity for the presence of a certain amount of 
particles passing a 100- and an 80-mesh screen, is a 
double one. Some material of this nature is required 
to produce a surface mixture which shall close up tightly 
under rolling and thus exclude water. It reduces the 
size, and to a certain extent, the volume of the voids 
between the larger sand particles which must be filled 
with asphalt cement and, in this sense, adds to the sta- 
bility of the mixture to a certain degree, as also does the 
finer material or filler which is employed in addition. 
The 100- and the 80-mesh particles are necessary to 
permit of the use of a sufficiently large percentage of 
filler to further accomplish this result and give stability 
to the mineral aggregate and to the asphalt cement. 
Unless the sand contains a large percentage of fine 
particles of 80- and loo-mesh size the filler which is 
added, if in sufficiently large amount to make the most 
desirable surface, will accumulate in balls and adhere to 
the coarser particles of sand in an irregular way, making 
it difficult or impossible to spread and compress the hot 



32 ASPHALT CONSTRUCTION 

material on the street satisfactorily. It will be observed, 
in another chapter, as illustrating this fact, that a mixture 
such as that laid on the Thames Embankment in London, 
which carries 17 or 18 per cent, of particles passing a 
200-mesh sieve, largely filler, contains at the same time 
30 per cent, of fine, 100- and 80-mesh, sand particles. 
Without the presence of the latter it would be impossible 
to use the amount of filler employed. It is found also 
that unless the percentage of filler is large the percentage 
of bitumen in the mixture cannot be carried at a high 
figure, as should be the case to enable the pavement to 
resist moisture. The importance of the sand grading is, 
therefore, plainly indicated. 

The character of the material composing the sand 
grains is, of course, a matter of importance. It should 
consist of hard quartz. The character of the surface 
of the grains cannot be neglected. It should be free 
from any adhesive ferruginous or argillaceous matter 
which would prevent the proper adhesion of the asphalt 
cement, that is to say, the sand should be clean. Even 
with clean sand grains there is a difference in the sand's 
behavior with bitumen, which may be compared to 
that of the surface of an ordinary sheet of glass and 
one of ground glass. The latter will hold a coating of 
bitumen well, and the other less satisfactorily, as can 
be easily understood. As a matter of fact sands from 
certain localities will carry less than 9 per cent, of bitu- 
men, whereas others, as those on the Pacific coast and 
in England, will carry over 11 per cent. The behavior of 
every sand in this respect can only be determined by trial. 

The shape of the sand grains has also a direct effect 
upon the character of the surface mixture. Too sharp 
a grain is not desirable and, on the other hand, one that 



THE MINERAL AGGREGATE 33 

is too round and resembles shot is more so because it is 
unstable. A medium sharp grain is desirable but the 
preference lies for the rounded grain rather than a sharp 
one, as the rounded grain produces a surface mixture 
which is more readily compressed on the street. 

Sands and their characteristics are discussed at great 
length in the writer's book ^^The Modern Asphalt Pave- 
ment/' and it is important that every one engaged in the 
construction of sheet asphalt pavements should be 
thoroughly familiar with this subject in order to be able 
to make a proper selection of material of this description, 
for good work. 

Aggregates Containing Fine Stone. — Aggregates of 
the type of which asphalt blocks are composed consist of 
an admixture to the fine material of small broken stone 
or pea grit. Aggregates of this . description are also 
employed for monolithic sheet work, and have become 
quite popular within the year 191 2, having been con- 
structed on a large scale. It is improper to call these, 
as is sometimes done, asphaltic concrete, as the stone is 
too small both in size and amount, to make it possible 
to regard the aggregate as concrete. The stone should 
constitute more than 50 per cent, of an aggregate, in 
order that it may be classed as a true concrete. The com- 
position of an asphalt block will average about as follows: 

Density of block 2 . 53 

Bitumen 7.3 



Passing 200 mesh 16 

Passing 10 mesh 39 

Passing 8 mesh 7 

Passing 1/4-in holes 26 

Retained 1/4-in. holes. . . 3 



1 00.0 per cent. 



34 ASPHALT CONSTRUCTION 

It appears that this aggregate consists to a large 
extent of particles of the size of sand and filler and about 
30 per cent, of pieces of stone retained on an 8-mesh 
screen, approximately 1/4 in. in diameter. Such, an 
aggregate is typical of a grit mixture. Of the character 
of such mixtures when combined with bitumen and laid 
in monolithic form more will be said in another place. 



CHAPTER VI 
FILLER OR DUST 

An impalpably finely ground mineral matter or dust 
is used as a filler in combination with sand to complete 
the mineral aggregate for surface mixtures in order to 
make the surface when compressed more dense, and to 
render the asphalt cement, which is one of the com- 
ponents, more stable and less susceptible to the high 
temperatures to which it may be subjected under the 
summer suns of our climate. It makes the surface, at 
the same time, less susceptible to water action, and less 
liable to displacement under travel. It is an important 
part of the mineral aggregate for many reasons, as giving 
it stability and, as shown by the writer's examination 
in the early years of the industry of the surfaces which 
proved to be satisfactory, it was the presence of a proper 
percentage of such material, in addition to the character 
of the sand, which made them so. 

In any filler it is the amount of material which is so 
impalpably fine as not only to pass a 200-mesh sieve 
but also to remain suspended in water for at least fifteen 
seconds, which is of value. The 200-mesh screen alone 
will not demonstrate its value. Anything which is so 
coarse as to simply pass the 200-mesh screen, will merely 
play the role of sand, and will be a poor sand at that. 
A material to be suitable for a filler should be ground so 
fine that at least 75 per cent, will pass a 200-mesh sieve 
and at least 66 per cent, of it remain suspended in water 
I 35 

i 



36 



ASPHALT CONSTRUCTION 



m 



These 
the 



of a definite temperature for fifteen seconds 
characteristics may be readily determined 
laboratory. Illustrating the conditions in various 
supplies of fillers the following data will serve: 



Test No 


75803 


75804 


75805 


75806 


71076 


75791 


Dust 


Lime- 
stone 


Trap- 
rock 


Port, 
cement 


Clay 


Marl 


Vol- 
canic 


Passing 200 mesh 

Passing 100 mesh 

Passing 80 mesh 

Passing 50 mesh 


84.0% 
14.0 
2.0 


81% 
18 
I 


74% 
19 

6 

I 

56.7 
123.5 


93% 
5 
I 
I 

87.8 
78.0 


92% 
4 
2 
2 

80.3 
78.0 


100% 


Eiutriation test, not 

settled in 15 seconds. 

Pounds per cubic foot 


71.3 
113. 7 


70.3 
112. 3 


98.2 
63.4 



It appears that in materials which may be used as a 
filler there is a decidedly smaller proportion of impalpably 
fine powder than of particles which will pass a 200-mesh 
sieve. 

Another important consideration in connection with 
materials in use as a filler is the volume weight of the 
pulverized material. In the table the data shows that 
this varies to a very great extent. The heavier the 
weight, the more desirable the filler is, as it contributes 
to the density of the surface mixture. 

The nature of the material that the filler is derived 
from is of importance. It has been found by service 
tests that the most desirable filler is a finely ground 



FILLER OR DUST 37 

Portland cement, and this should always be used where 
the surface is to be subjected to heavy travel or to exces- 
sive moisture. The filler for ordinary use is usually a 
ground limestone of the desired fineness. Clay could 
be used as a filler were it not for the fact that it is so light 
as to make the loss in mixing the dry mineral aggregate 
excessive. 

The amount of filler which is added to the sand should 
be such that a finished surface mixture for ordinary 
purposes will contain at least lo per cent, of 200-mesh 
particles. It should reach 18 per cent, in surfaces made 
with fine sand which are to withstand the heaviest traffic 
and the most trying climatic conditions. As has been 
said previously the use of such high percentages of filler 
requires a sand carrying a proper. amount of fine par- 
ticles, to prevent the filler from segregating into balls in 
the hot mixture. The amount of filler in actual use will 
vary depending on whether the asphalt employed contains 
mineral matter or not. As Trinidad asphalt cement 
contains a percentage of clay and impalpably fine quartz 
acting as a natural filler it is not necessary to add as 
much artificial filler as in the case of Bermudez asphalt, 
which is a nearly pure bitumen. In turning out a 
Trinidad surface mixture, therefore, but 80 lb. per 9 
cu. ft. box may be necessary with Trinidad for ordinary 
work whereas 100 lb. or more must be used with a 
Bermudez asphalt cement. Regard must also be given 
to the fact that the density of Portland cement is much 
greater than limestone, and a greater weight of the former 
material than of the latter must be used if the same 
volume of filler is to be pro\T[ded. 

Finally it should be said that upon the judicious use 
of filler the entire success of a sheet asphalt surface may 



38 ASPHALT CONSTRUCTION 

depend. The amount should not be reduced below 
the limit suggested and it can be kept at the highest 
figure that the sand permits to the greatest advantage. 
On the other hand, an excess of filler with a poorly graded 
sand, will make the hot mixture so tough that it cannot 
be easily raked out and spread on the street. On this 
account an adequate amount is impossible with such 
sands. 

In turning out a close binder, filler is not as essential, 
since the stone gives stability to the mixture, but if an 
asphaltic concrete surface is being constructed, filler is 
essential, and should be used in such proportions that 
it will be present in an amount corresponding to that 
which would be required by the sand present, considered 
as an aggregate of a sheet asphalt surface mixture. 



CHAPTER VII 
NATIVE BITUMENS 

A mineral aggregate which is above criticism being 
available, the character of the sheet asphalt surface 
which is produced, will depend upon that of the asphalt 
which is used as a binding or cementing material, and 
upon the manner in which it is manipulated. 

A native bitumen is one found in nature consist- 
ing of a mixture of hydrocarbons and their deriva- 
tives, which may be gas, a liquid, a viscous liquid 
or a solid. If solid it melts more or less readily on 
the application of heat, and is soluble in turpentine, 
chloroform, carbon disulphide and similar solvents, as 
well as in the heavy petroleum oils. One of the solid 
forms of native bitumen is asphalt. The asphalts are 
characterized by various physical and chemical proper- 
ties, and by their behavior when subjected to certain 
conditions which have been defined. The most impor- 
tant of these are in detail as follows: 

PHYSICAL PROPERTIES 

Specific gravity, 77° F. 77° F. Original substance, 

dry 
Specific gravity, 77° F. 77^ F. Pure bitumen 
Color of powder or streak 
Luster 
Structure 

39 



40 ASPHALT CONSTRUCTION 

Fracture 

Hardness, original substance 

Odor 

Softens 

Flows 

Consistency, penetration at 77° F. 

Ductility in centimeters 

CHEMICAL CHARACTERISTICS 

Original substance. 

Loss, 212° F., one hour 
Dry substance. 

Loss 325° F., five hours 

Character of residue 

Consistency, penetration of residue at 77° F. 
Bitumen soluble in carbon disulphide, air temperature 
Inorganic or mineral matter 
Difference 
Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 

This is per cent, of total bitumen 

Per cent, of soluble bitumen removed by H2SO4 

Per cent, of total bitumen as saturated hydrocarbons 
Carbenes: 

Bitumen insoluble in carbon tetrachloride, air 
temperature 
Bitumen yields on ignition : 

Residual coke, ash free 
Sulphur 
Paraffine scale 
Ultimate composition 



NATIVE BITUMENS 41 

Experience and long-time service tests have demon- 
strated that certain native asphalts, such as those from 
the Trinidad and Bermudez lake deposits, have been 
most successfully used in the production of an asphalt 
cement for the construction of pavements and road sur- 
faces, and more so than any other solid bitumens. The 
characteristics of these materials may be taken, there- 
fore, as a standard. They are to be found for each of 
these asphalts on a subsequent page. They are, of 
course, somewhat modified when they are combined 
with a flux to produce an asphalt cement. Cement 
made from Trinidad and Bermudez asphalt is charac- 
terized by a definite specific gravity in each case, by a 
certain ductility as determined by a conventional test, 
by containing but little volatile matter so that when 
the cement is heated for some time at the temperature 
at which it is used the loss does not exceed a small per- 
centage and the consistency is not reduced to an alarm- 
ing degree, by the fact that it has a certain viscosity 
with which other asphalt cements can be compared, 
and that it contains a large amount of sulphur, which 
has an important bearing on its stability. These 
cements, in addition, possess adhesive binding and 
cementing properties and are not short, cheesy and oily. 
They do not harden excessively when exposed to low 
temperatures or become too liquid under the summer 
sun. They do not contain a large portion of light oils 
volatile during the period in which the material is main- 
tained in a melted condition or on mixing with a hot 
mineral aggregate. They have great viscosity at atmos- 
pheric temperatures but become sufl&ciently mobile at 
higher temperatures to mix satisfactorily with the 
mineral aggregate. 



42 ASPHALT CONSTRUCTION 

Residual pitches prepared from asphaltic or semi- 
asphaltic petroleums by industrial processes, are gener- 
ally termed asphalts, as well as the solid native bitu- 
mens, using this designation in its broadest commercial 
sense. Owing to the different kinds of petroleum in 
which they originate, they are of a very varied charac- 
ter, and at the same time, owing to the greater or less 
care with which they are prepared, they are far from 
uniform. As yet, it has not been demonstrated by long- 
time service tests that they are the equals of the solid 
native bitumens. Where they have been used the cost 
of maintenance is considerably greater than that of the 
native asphalts, but it must be remembered that the 
skill and judgment with which any asphalt is manipu- 
lated is of equal importance as its character, and the 
residual pitches may not have been used as skillfully as 
has been the case with the native material. 

Trinidad asphalt, as it is well known, has been in use 
in the construction of sheet asphalt pavements since 
1876, when it was first used on any extended scale on 
Pennsylvania Avenue in Washington, D. C. There are 
many other striking examples of the behavior and dura- 
bility of this material in existence at the present time. 
One of them is the sheet asphalt surface, which has been 
mentioned on a previous page, on Vermont Avenue in 
Washington, D. C, between H and I Streets. This 
surface was constructed in 1879 and is in existence to- 
day, 1 91 3, after thirty-four years use, and, even now, is 
in a condition which permits the conclusion that it will 
give many years further service. The maintenance in 
the period between the date of its construction and 1910 
was only 9.98 cents per superficial square yard. Another 
example is the surface which was constructed on Fifth 



j 



NATIVE BITUMENS 43 

Avenue in New York City in 1896-97, and which has with- 
stood with great satisfaction the enormous travel to which 
it has been subjected on that street. On some of the 
business streets of Chicago subjected to the heavier com- 
mercial traffic, such as Market, Franklin and Quincy 
Streets, Trinidad asphalt surfaces have proved as last- 
ing as any smooth surface pavement would have been 
under the same conditions. A most striking example 
of the ability of a well-constructed Trinidad asphalt 
surface to resist the severe conditions existing in the 
climate of England and the heavy travel of a London 
thoroughfare, will be seen on the Victoria Embankment 
in London. This surface, which is of world-wide repute, 
has demonstrated the fact that it has been able to meet 
the conditions existing at that point in competition 
with many other forms of construction, with entire 
success. It has been pronounced by an engineer of 
the Road Board of Great Britain to be a type of the 
most successful form of bituminous road surface. 

The successful use of Trinidad asphalt may be at- 
tributed to the entire uniformity of the material as it 
is found in the so-called lake deposit in the Island of 
Trinidad. Every cargo of the asphalt which has been 
brought from that point during the last thirty-six years 
or more, has been found, by observation of the writer, 
to be practically like another. This is an extremely 
important feature, as, when its manipulation is once 
learned, there is no necessity for making changes in it 
to obtain uniform results. Among its other desirable 
properties are its stability, under which may be included 
its resistance to high temperatures under manipulation 
and permanence of consistency, its lack of suscepti- 
bility to solar radiation in the street during the summer, 



44 ASPHALT CONSTRUCTION 

and the fact that it carries, intimately mixed with it 
by nature, a large percentage of fine mineral matter of 
the most desirable character as a filler. 

Bermudez asphalt is another form of native bitumen 
or asphalt, which is found in Venezuela. It differs 
from the Trinidad asphalt in carrying no admixture of 
mineral water, being a nearly pure bitumen. The de- 
posit is not as uniform as that which is found in Trini- 
dad, and the material as dried or refined, varies from 
time to time in its consistency. It hardens on heating 
through loss of volatile oils more than the Trinidad 
material, and its manipulation requires greater care to 
produce a satisfactory asphalt cement. It possesses 
certain properties, however, which makes it preferable 
to Trinidad asphalt in that it melts to a thinner liquid 
owing to tiie absence of mineral matter, and on this 
account permits of easier manipulation. At the same 
time it lacks the stability of Trinidad asphalt and suf- 
fers more from abuse in melting and mixing with hot 
aggregates. Bemudez asphalt has been subjected to 
service tests since 1893 and when combined with a 
suitable mineral aggregate has given entirely satisfactory 
results, surfaces constructed with it being of a durable 
nature. It has been much used in the last four or five 
years as a cementing material for bituminous broken- 
stone highways, and has proved extremely successful 
as applied to this form of construction, owing to the fact 
that it can be used in the penetration process with much 
greater ease than a similar binding material made from 
the more viscous Trinidad asphalt, although the Trini- 
dad asphalt is equally satisfactory, as used in New 
York State, when once it is properly introduced into 
the road surface. 



NATIVE BITUMENS 45 

The two asphalts which have been mentioned, Trini- 
dad and Bermudez, have been tried out for such long 
periods of time that their reputation as a satisfactory 
binding material is established. None of the asphaltic 
materials, the products of asphaltic petroleum manipu- 
lated by industrial processes, have been tried out for 
the same length of time, or at least, there is no surface 
in existence to-day of the same age. They have not 
been shown to possess the durability of the native lake 
bitumen. For this reason, this handbook is confined 
to the use alone of the two materials mentioned, 
although of course, many of these directions can be 
applied to the use of other materials. 

Trinidad Lake Asphalt. — ^Crude Trinidad asphalt is 
an extremely uniform mixture or emulsion of gas, water, 
fine sand, clay and bitumen combined in the following 
proportions: 

Bitumen .... 39.3 per cent. 

Mineral matter 27.2 

Water of hydration of clay. 7^.2^ 

Water and gas, loss at 325° F 29.0 



98 . 8 per cent. 

It has been found to have practically the same compo- 
sition in the entire deposit, having a surface of more than 
1,000 ft. in diameter and a depth of over 135 ft. In 
preparing it for use in the paving industry it is subjected 
to so-called refining which amounts really to drying the 
material and removing the water entering into the 
emulsion which composes the crude material. Some of 
the characteristics of the refined material are as follows: 



46 ASPHALT CONSTRUCTION 

REFINED TRINIDAD ASPHALT 

PHYSICAL PROPERTIES 

Specific gravity at 77° F i -397 

Melting-point 230'' F. 

Color of powder or streak Blue black. 

Luster Dull. 

CHEMICAL CHARACTERISTICS 

Loss at 325° F. for five hours.. . 0.8 per cent. 

Character after heating Smooth. 

Bitumen soluble in CS2. ....... 55.8 per cent. 

Mineral matter 36.3 

Difference 7.9 

100. o 

Bitumen soluble in 88° naphtha 38.0 per cent. 
This is per cent, of total bitumen j66 . 2 
Bitumen yields on ignition: 
Residual coke, ash free ...... 12.7 

The refined asphalt, although hard and rather brittle 
when struck a sharp blow, possesses sufficient viscosity 
to flow slowly under pressure at low temperatures. 
To make it available as a binding material for pave- 
ments and road surfaces, it is necessary to bring it to the 
proper consistency by mixing it with a heavy petroleum 
oil or flux of a nature which will be described later. 
This combination is known as asphalt cement. 

Bermudez Asphalt. — -Crude Bermudez asphalt is re- 
fined in the same way as the crude Trinidad material, 
that is to say, it is heated until the water is driven off. 
The refined material is much softer than the refined 
Trinidad asphciltr It varies in degree depending on the 



NATIVE BITUMENS 47 

part of the lake deposit from which the crude asphalt is 
taken. Some of the characteristics of the supply which 
has been marketed in 191 2, are as follows: 

PHYSICAL PROPERTIES 

Specific gravity at 77° F i .075 

Melting-point 183° F. 

Color of powder or streak Black. 

Luster. Bright. 

CHEMICAL CHARACTERISTICS 

Loss at 325° F. for five hours. . . 2.8 per cent. 

Character of residue Smooth. 

Bitumen soluble in CS2 92 . 5 per cent. 

Mineral matter 4.9 

Difference ^ 2.6 

100. o 

Bitumen soluble in 88° naphtha 64.0 per cent. 

This is per cent, of total bitumen 69 . 2 
Bitumen yields on ignition: 

Residual coke, ash free 13 .4 per cent. 

As the asphalt is softer than that from Trinidad the 
amount of flux with which it must be combined, although 
a certain amount is always necessary, is less than is 
employed with the harder asphalt, as will appear later. 
It also hardens more rapidly than a Trinidad asphalt 
cement on being maintained in a melted condition, 
especially with agitation, for an extended period of time 
and requires more careful watching on this account in 
order that it may eventually have a proper consistency 
as it exists in the finished pavement. 



CHAPTER VIII 
FLUXES 

For the production of an asphalt cement of suitable 
consistency for use in sheet asphalt pavements or as a 
road binder, the refined native asphalt must be combined 
with heavy oils, or residues from the distillation of various 
petroleums, which are known as fluxes. These fluxes 
are as varied in character as the petroleums from which 
they are derived, and they vary from year to year as the 
available supplie.:. of petroleum for their production vary. 

For many years the fluxes or residaums originated in 
the paraffine petroleums of the East, but this source of 
supply is unavailable at the present time. Of the flaxes 
which areon the market in 191 3 none of them originate 
in a straight paraffine petroleum. They are derived from 
semi-asphaltic and asphaltic oils which have the char- 
acteristics given in the following table. Many of them 
are available only in a limited amount commercially. 

The fluxes in the table differ essentially as regards 
specific gravity, the amount of paraffine scale which 
they contain, the residual coke which they yield on 
ignition, and in the percentage of bitumen which is 
insoluble in 88° naphtha. The more asphaltic the flux 
the more residual coke it yields and the more material 
insoluble in naphtha it contains. 

On account of these great variations, it is most impor- 
tant that any one preparing an asphalt cement should be 
thoroughly informed in regard to the character of the flux 

48 



NATIVE BITUMENS 



49 



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50 ASPHALT CONSTRUCTION 

which is at hand before attempting to use it. In the 
case of a flux of lower gravity a smaller amount is 
required to produce an asphalt cement of suitable con- 
sistency for paving purposes than of a heavier one. 
About 20 lb. of the lighter flux are required for each 
100 lb. of refined Trinidad asphalt, and about 7 lb. with 
the present supply of Bermudez refined asphalt. A 
much larger amount of the heavy asphaltic fluxes is 
necessary owing to their greater density and viscosity. 
This may reach as much as 40 or 50 lb. per 100 of as- 
phalt instead of 20, as in the case of the paraffine fluxes. 

It must be remembered, however, that the character 
of the supply of fluxes which are available on the market 
is very variable from year to year, owing to the fact that 
the crude petroleum which is available for their produc- 
tion is obtained from different fields at different times, 
and that a supply which may be entirely satisfactory at 
one time may not be available at another. As an 
example may be cited the fact that ten years ago one of 
the best fluxes ever used in the paving industry was 
made from Beaumont petroleum. The product of this 
field, however, was soon exhausted, and recourse was 
necessary to other fields for the crude material for 
manufacturing flux. For this reason no definite advice 
can be given in a printed publication as to how the flux 
supply can be handled at any time in the future. This 
must be carefully studied on an experimental scale in 
the laboratory before attempting to employ a new 
source of supply in practice. 

In view of the facts which have been presented, it is 
evident that a specification which may provide for a 
satisfactory flux at any given time, will not serve that 
purpose in some subsequent year. In the present 



FLUXES 51 

status of the petroleum industry in the United States 
it is evident that there is no source of constant supply 
of flux and that the matter must be taken up anew every 
year. 



CHAPTER IX 
ASPHALT CEMENT 

In the preparation of an asphalt cement the refined 
material and flux must be thoroughly combined to pro- 
duce a satisfactory material. The refined asphalt must 
be carefully weighed, melted and raised to a temperature 
of at least 325° F. and not above 350° F. The flux 
should preferably be heated with steam coils, or other- 
wise, to a temperature of 150° to 200° F. for if it is run 
while cold into the melted asphalt, the two will mix 
slowly, and, unless much time is given the mixing may 
not be thorough. While the oil is being run in, agitation 
should be provided by means of a current of air or steam 
admitted, preferably through pipes at the bottom of the 
melting tanks. Steam is better, because air has a ten- 
dency to harden and also change the properties of the 
cement, in the same manner that occurs when blown pro- 
ducts are prepared. The flux is usually supplied in tank 
cars. It is well to observe that there is no water in the 
tank cars before the oil is drawn into the supply tank, as it 
will cause foaming and much delay in making the cement. 
For the same reason if steam is used for warming the oil 
in the tank car, care should be taken that no water is 
introduced in that way through loose connections or 
leaky coils. 

The agitation should be kept up for some hours 
until the asphalt cement is homogeneous and during the 
entire time that it is in use, in the case of Trinidad 

52 



ASPHALT CEMENT 53 

asphalt to keep the mineral matter which it contains sus- 
pended in a uniform manner, and in the case of Bermudez 
to prevent overheating of the material where it is in 
contact with the hot sides of melting tanks, especially 
over fire, where they are not heated by steam coils. 
Under the most favorable circumstances three hours 
agitation is necessary and, with inferior agitation, a 
much longer time may be required. The character of 
the cement can be determined by pouring some of it into 
a pail of cold water and examining it on cooling. If 
any free oil is apparent more agitation is necessary. 

When the asphalt cement is homogeneous, the next 
step is to determine whether the consistency is that 
which is desired. The ordinary method is by the use 
of the penetrometer, an instrument carrying a No. 2 
cambric needle weighted with 100 grm. which is brought 
into contact with the surface of some of the asphalt 
cement in a tin box which has been brought to the 
standard temperature of 77° F. by being immersed in water 
for a considerable period of time. The needle is released 
and allowed to act five seconds. The distance to which 
it penetrates is read off by the movement of an indicator 
upon a circular scale upon a dial, each division of which 
represents a hundredth of a centimeter, and is generally 
referred to as a point. A cement may, therefore, be said 
to penetrate 40, 50 or 60 points. The consistency is varied 
somewhat, but very slightly, according to the conditions 
to be met. Ordinarily a penetration of 50 or 55 should 
be used with a well-graded sand aggregate containing 
plenty of filler. With a coarser and inferior one a harder 
cement must be employed. Testing the cement for 
consistency should be undertaken daily if the lot which 
is being used is not exhausted. Asphalt cement will 



54 ASPHALT CONSTRUCTION 

harden up a number of points if maintained in a melted 
condition overnight or for some time during bad weather. 
The extent will depend upon the method by which it is 
heated, whether over an open fire or by means of steam 
coils, and also upon the degree of agitation to which it is 
subjected. Too powerful an agitation is injurious. To 
correct the effect of agitation a certain amount of flux 
must be added daily, according to the judgment of the 
operator or plant foreman, to maintain the asphalt cement 
at the proper consistency. 

The consistency of the cement can also be checked by 
noting the length to which a small cylinder of it made in 
a mould designed for the purpose, will flow on a corru- 
gated brass plate in comparison with a cylinder of 
standard material when exposed in a closed box heated 
to the flowing point of the cement with a steam coil. 

The consistency has been regulated at times very 
satisfactorily in the past by experienced plant foremen, 
by chewing the cement. This is more available in the 
case of Trinidad asphalt than Bermudez, but can be used 
with the latter by an expert. With other aspiialts it is 
not reliable. 

All that has been said in regard to asphalt cements for 
sheet asphalt surfaces applies equally well to those which 
are used in asphaltic concrete and for bituminous broken- 
stone roads, except that the consistency is necessarily 
somewhat softer for concrete and too soft for the con- 
venient use of the penetrometer in the case of road 
binders. For an asphaltic concrete a penetration of 
about 90 is desirable, and 150 for broken-stone work, 
whether conducted by the penetration or mixing process. 
The softer cements aie possible in these cases because of 
the greater stability of the mineral_aggregate of the 



the i 



ASPHALT CEMENT 55 

concrete and of the stone in a broken-stone surface, and 
are used because the softer the cement is the more 
satisfactory the surface will be at low temperatures. 
The degree of softness is only limited by its susceptibility 
to the high temperatures to which it is subjected under a 
summer's sun. The native lake asphalts permit of the 
use of a much softer binding material in both cases than of 
the industrial products, which are most susceptible to the 
heat of the snn, and are drawn to the surface by it with 
unsatisfactory results, the surfaces ^^ bleeding'' as it is 
called. 



CHAPTER X 
SURFACE MIXTURES 

Having considered individually the components which 
make up the various forms of asphalt surface mixture, 
their combination in a rational way and the reasons for 
so doing may be taken up. 

Sheet Asphalt Mixture. — A sheet asphalt surface 
mixture consists of three essential components, a well- 
graded sand, sufficient filler and an asphalt cement of 
proper consistency. In the early days of the industry 
the surfaces which were constructed were of types which, 
while they withstood very satisfactorily the moderate 
travel to which they were subjected in such cities 
as Washington and Buffalo, were not suited to the 
more intense conditions to which such pavements are 
exposed to-day in the larger cities and, frequently, such 
surfaces were not satisfactory even under the less trying 
conditions. The variation in the composition of sheet 
asphalt surfaces laid in various cities before 1894 was 
large and is shown in the following table, taken from the 
writer's book "The Modern Asphalt Pavement." 

There is no uniformity in the grading of the mineral 
aggregates of these mixtures, and in many cases there is 
a deficiency of bitumen, the percentage varying from 

56 



SURFACE MIXTURES 



57 



SHEET ASPHALT SURFACE MIXTURES, LAID BEFORE 
1894 



Mineral aggregate passing mesh 




200 


100 & 80 


50&40 


9.72 


6.45 


42.06 


14.50 


9.06 


38.30 


8.38 


9.48 


41.26 


10.87 


12. 12 


60. 10 


10.93 


12.77 


49.06 


II. 27 


15.34 


52.59 


12.13 


16.39 


34.14 


12.15 


22.01 


37.58 


14.46 


35.32 


26.19 
31.31 


13.10 


25.92 


II. 91 


29.19 


39.38 


11.32 


3O..53 


44.68 


9.33 


35-95 


38.83 


12.80 


41.98 


24 -93 


11.63 


21.61 


40.03 


13.0 


26.0 


34.5 



30, 
20, 

&IO 



Total 



Washington. . 

Louisville 

Newark 

St. Louis 

Youngsto wn . 
New Orleans. 
New York. . . 
Scran ton. . . . . 

Boston 

Kansas City. 
Schenectady. 

Buffalo 

Chicago 

Omaha 



Average. 



I For comparison: 

j Standard mixture' 10. 5 



10. 29 
8.91 
8.81 
9.61 
9.06 

9.87 
10.97 
10.64 
11.75 

9.85 
10.32 

9.65 
9.24 

9.44 
9.89 



31.48 

29.23 

32.07 

7.30 

18.18 

10.93 

26.37 

17.62 

12. 28 

19.82 

9. 20 

3.82 

6.65 

10.85 

16.84 



16.0 



100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 

100% 



100% 



8.8 to II. 7, not from a desire to] reduce the] amount 
but because the mineral aggregate would, probably, not 
carry more. The mineral aggregate has evidently or- 
iginated in each case in a local sand without regard to 
its character or suitability for the purpose for which it 
is used. As compared with what is now considered a 
standard grading the finer sand, 100 and 80 mesh, is 



58 ASPHALT CONSTRUCTION 

deficient in many cases, and is too great in amount in 
others. The percentage of coarse particles, which gives 
the surface stability and roughness, if present in the 
proper amount, but which renders it open and porous if 
present in too large a quantity, was, in several cases, not 
well regulated. The Washington, Louisville, Newark 
and New York mixtures contained too large a proportion 
of coarse, and the Boston, Omaha and Chicago mixtures 
too much fine sand. The great variations show how 
little attention was paid in the early days of the industry 
to the matter of selection of sand. The percentage of 
filler in the mixtures appears to have been in many cases 
sufficient, but this percentage is generally due to fine 
2oo-mesh sand and not to the presence of an added filler, 
as in those days only about 4 per cent, was used. Some 
of the mixtures, therefoie, would not carry enough 
bitumen. Others were unstable if they contained an 
amount considered suitable to-day, and some cracked 
or disintegrated when the bitumen was low. 

After it had become apparent to the writer, as long ago 
as 1894, from a study of the surfaces which had been 
laid previous to that time, that the mineral aggregate 
must be more carefully regulated if uniform success was 
to be attained, an attempt was made to do so. Mixtures 
were turned out in 1897 which showed greater uniform- 
ity, as appears in the following table, taken from the 
same source as the preceding one, although the grading 
was not ideal in every respect owing to local limitations. 
Notwithstanding the latter fact, all of these mixtures, 
with the improved grading of the aggregate and more 
filler, carried over 10 per cent, of bitumen. They average 

The results show the possibility, with care, of bringing 



I 



SURFACE MIXTURES 



59 



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60 



ASPHALT CONSTRUCTION 



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SURFACE MIXTURES 61 

about some uniformity in the production of asphalt 
surface mixtures. 

The penetrations as given in the last column of the 
table are in units of the old Bo wen penetration machine 
which are, approximately, 20 points higher than the 
readings of the present instrument. The average pene- 
tration of the cement would be, therefore, only 38 as now 
determined. This would, to-day, be regarded as much 
too hard since experience has shown us that, with a 
better-graded mineral aggregate a softer cement can be 
used, one 20 points softer than in the year under con- 
sideration. The readings given in the table may, there- 
fore, be regarded as suitable penetrations, to-day, with 
the instrument now in use, for new work. 

Probably the improvement which has been made in 
sheet asphalt surfaces in recent years is to be attributed 
to the fact, as far as the higher percentage of bitumen 
which they contain is concerned, that a well-graded 
mineral aggregate will carry a larger percentage. Too 
small an amount reduces the strength of the material, 
especially at low winter temperatures, and in addition, 
makes it more susceptible to water action. 

As illustrating the points to be given careful considera- 
tion in the preparation of a satisfactory surface mixture 
some of the writer's experiences and the results of his 
studies may be cited. 

In 1894 an attempt was made to construct a Trinidad 
sheet asphalt pavement on the Kings Road in Fulham, 
London, England, on the lines which had been followed 
previous to that time in America. The results were not 
successful as the mixture scaled under heavy travel in 
the damp climate at that point. It analyzed as follows: 



62 ASPHALT CONSTRUCTION 

KINGS ROAD, FULHAM, LONDON, 1894 

Bitumen lo.o 

Passing 200 mesh 7.4 

Passing 100 mesh 15.9 

Passing 80 mesh 11 . 4 

Passing 50 mesh 11. i 

Passing 40 mesh 24.0 

Passing 30 mesh 12.2 

Passing 20 mesh 5.0 

Passing 10 mesh 3.0 

100. o 

After a study of the conditions existing there, and the 
necessity of carefully regulating the mineral aggregate, 
a satisfactory mixture was turned out in 1896, which had 
the following composition: 

KINGS ROAD, FULHAM, LONDON, 1896 

Bitumen 10.8 

Passing 200 mesh 13.6 

Passing 100 mesh 7.3 

Passing 80 mesh 22.5 

Passing 50 mesh 25.5 

Passing 40 mesh 8.9 

Passing 30 mesh : . . 6.6 

Passing 20 mesh 3.0 

Passing 10 mesh 1.8 

100.0 

A comparison of the two mixtures reveals at once why 
one was satisfactory and the other not. While the sand 
in both cases had an acceptable grading, the mixture in 



SURFACE MIXTURES 63 

1894 was deficient in filler, carrying only about one-half 
as much as that of 1896. In consequence of the lack of 
filler the 1894 mixture carried nearly i per cent, less 
bitumen. Further studies of the London conditions have 
led to the production of a mixture at that point which 
now carries as much as 17 per cent, of filler and 11.5 per 
cent, of bitumen, which is, correspondingly, more satis- 
factory. Reference to this mixture will be made later. 
The 1896 surface constructed with the mixture, the com- 
position of which has been given, resisted fairly satis- 
factorily the trying climatic conditions and the heavy 
travel to which it was subjected in London, but required 
considerable maintenance. This was, no doubt, due to 
a smaller percentage of filler and bitumen than in subse- 
quent mixtures and, probably, also to the fact that it 
was placed upon and only supported by an ordinary open 
binder which was inadequate. In 1906 under the 
author's supervision, the more satisfactory mixture 
which was referred to, was laid upon an asphaltic con- 
crete close binder, on the Thames embankment, and has 
proved to be an extremely satisfactory piece of work. It 
was made with materials in the following proportions, 
and had the composition given below: 



THAMES EMBANKMENT, 1906 

Asphalt cement (lb.) 152 

Dust (Portland cement) (lb.) 170 

Sand 600 

Per cent. A. C 16.5 

Per cent, dust 18.4 

Per cent, sand 65.1 

100. o 



64 ASPHALT CONSTRUCTION 

ANALYSIS 

Bitumen ii . 5 

Passing 200 mesh 17.5 

Passing 100 mesh 7.0 

Passing 80 mesh 23 . o 

Passing 50 mesh 32.0 

Passing 40 mesh 6.0 

Passing 30 mesh 3.0 

Passing 20 mesh 0.0 

Passing 10 mesh 0.0 



100. o 



Attention has been called to the high percentages of 
bitumen and filler, the former being possible because 
of the presence of the latter and the large amount of 
filler being possible only because of the very fine sand.* 
The mixture, it will be seen, may be considered as being* 
deficient in coarse material and would, no doubt, be im- 
proved in certain directions if more coarse sand were 
present, but in this case it would not carry as high a 
percentage of bitumen and on this account might not 
prove as satisfactory in a moist climate like that of 
London. 

After the work in London in 1896, the Fifth Avenue 
pavement in New York between 9th and 59th Street 
was laid by the writer in 1896-97. The average compo- 
sition of the mixtures laid in these two years is given 
in the following table for comparison with that of the 
London mixture: 



SURFACE MIXTURES 



65 





FIFTH AVENUE, 


NEW 


YORK 


CITY 










Passing mesh 




Bitu- 
men 


200 


100 


80 


50 


40 


30 


20 


10 


1896 


10.8 


15.4 


lO-S 


10.7 


22.3 


10.9 


8.9 


4.9 


5.6 


1897 


10.6 


17.4 


12.3 


II. I 


23.3 


8.8 


8.0 


4.7 


^•7 



For comparison 



London, 1896 
London, 1906 



10.8 

II. 5 


13.6 
17.5 


7.3 
7.0 


22.5 
23.0 


25.5 
32.0 


8.9 
6.0 


6.6 
3.0 


3.0 
0.0 



1.8 

0.0 



Comment on the sands composing these mixtures 
has been made in the chapter relating to mineral aggre- 
gates, but the data in regard to the completed mixtures 
show their desirable features. They carry a proper 
percentage of bitumen, over 10.5 per cent., a fair per- 
centage of filler, a satisfactory amount of sand of 100- 
and of 80-mesh size, and a considerable percentage of 
coarse material, 10, 20 and 30 mesh. In the latter 
respect they are perhaps preferable to the Thames em- 
bankment mixture of 1906. and correspond more closely 
with the London mixture of 1896. The Fifth Avenue sur- 
face has proved most satisfactory under the conditions to 
which it has been exposed. A more detailed account 
of the mixture and these conditions are contained in 
an article published by the writer in the Engineering 
Record for January 4, 19 13, to which the reader is 
referred. 

How far the t5^e of mixture laid on Fifth Avenue in 
New York in 1896-7 has been departed from in recent 
years, owing to the fact that the sand supplies available 



66 ASPHALT CONSTRUCTION 

in that city are no longer the same as in that year, and 
because of the fact that such a standard grading is not j 
demanded by municipal officials, may be seen from 
data in regard to the composition of a typical mixture 
laid in the Borough of Manhattan in 191 2: 

Bitumen 10.6 

Passing 200 mesh 13 .4 

Passing 100 mesh 8.0 

Passing 80 mesh 8.0 

Passing 50 mesh 26.0 

Passing 40 mesh 1 1 . o 

Passing 30 mesh 15.0 

Passing 20 mesh 5.0 

Passing 10 mesh 3.0 

100.0 

On comparison of the composition of this mixture 
with that of the Fifth Avenue mixture given on a pre- 
ceding page, it appears that it is deficient in fine sand 
of 100- and 80-mesh size, and carries 23 per cent, of | 
10-, 20-, and 30-mesh grains, as compared to 16.4 per 
cent, in the mixture laid on Fifth Avenue in 1897. It 
is a coarser mixture. It complies with the specifica- 
tions of the highway department of the borough, which 
are drawn to meet the possibilities as far as the sand 
supplies are concerned which now exist in New York. 
A more satisfactory sand would have to be brought 
from a long distance, and would increase the cost of 
the pavement to some extent, something which the 
engineers do not consider justifiable. In the most re- 
cent specification, that for 1913, the requirements for 
the mineral aggregate in the Borough of Manhattan, 
are as follows: 



SURFACE MIXTURES 



67 





Percentage of total mixture as 




laid 


Mineral aggregate 








Medium traffic 


Heavy traffic 




mixture 


mixture 


Retained by lo-mesh sieve 


None 


None 


Passing lo-mesh sieve, retained 


10 to 35% 


10 to 30% 


by 40-mesh sieve. 






Passing 40-mesh sieve, retained 


20 to 55% 


20 to 55% 


by 80-mesh sieve. 






Passing 80-mesh sieve, retained 


10 to 30% 


13 to 30% 


by 200-mesh sieve. 






Passing 200-mesh sieve 


12 to 18% 


13 to 20% 
10 to 12.5% 


Bitumen 


9.5 to 12.5% 


Penetration of asphaltic cement. . 


45 to 65 


40 to 55 


Filler 


Stone dust or 
Portland 


Stone dust or 




Portland 




cement. 


cement. 



In 1900 a sheet asphalt surface was laid in Paris, 
France, which was still in satisfactory condition in 191 2, 
and was of the character shown by the following data: 

AVENUE VICTORIA, PARIS, 1900 

Bitumen 10.9 

Passing 200 mesh 15.8 

Passing 100 mesh 14.6 

Passing 80 mesh 18.8 

Passing 50 mesh 28. 2 

Passing 40 mesh 5.8 

Passing 30 mesh 3.4 

Passing 20 mesh 1.5 

Passing 10 mesh i . o 

100. o 



68 



ASPHALT CONSTRUCTION 



The mineral aggregate was composed of the mixture 
of three sands which sifted as follows: 

PASSING MESH 





200 


100 


80 


50 


40 


30 


20 


10 


No. I 


10. 
1.0 
2.0 


78.0 
7.0 
6.0 


7.0 
430 
13.0 


4.0 
48.0 
28.0 


I.O 

1.0 
26.0 








No. 2 








No. 3... 


12.0 


10. 


3.0 



The above sands were combined in the proportions of 
I part No. I, 3 parts No. 2 and 4 parts No. 3. Portland 
cement was used as a filler. The mixture was made in 
the following proportions: 



Sand 700 lb. 

Portland cement 140 lb. 

Asphalt cement (Bermudez) 112 lb. 



The preceding mixture is typical of one constructed 
to meet the trying conditions encountered in Paris, 
that is to say, winters when pavements are not dry 
during the entire season, and at that time, 1900, 
heavy horse-drawn omnibus travel. 

The surface mixtures laid in London, Paris and on 
Fifth Avenue, New York, have been cited as concrete 
examples of types which will withstand heavy travel. 
The pavement on the Thames embankment is, without 
doubt, the one which has met the most trying conditions 
in the most satisfactory manner. The reason that it 
has done so is plainly due to the fact that it has a rigid 



^ 



SURFACE MIXTURES 69 

foundation, its mineral aggregate is fine, it carries a very 
large percentage of filler, 17.5, consisting of Portland 
cement, and in consequence a very high percentage of 
bitumen, 11.5, a possibility due to the fineness of the 
aggregate. It is, of course, an expensive mixture and 
one that would not be used unless difficult conditions 
were to be met, but it points to the necessity of high 
percentages of filler and bitumen in sheet asphalt surface 
mixtures to make them resistant to dampness and heavy 
travel. 

In ^^The Modern Asphalt Pavement,'' published by 
the writer some years ago, the following attempt at 
explaining the points to be observed in constructing a 
surface mixture in a rational way, made in 1896 in a small 
pamphlet prepared for the use of plant foremen and 
superintendents, was reprinted. It is still useful for the 
purpose for which it was originally intended. 

'^With the object of explaining to the practical man, 
the superintendent or yard foreman, the features of such 
a standard mixture it was considered from the point of 
view of consisting of a mineral aggregate composed of 
sand and dust and a proper percentage of bitumen. The 
mineral aggregate must be regarded as being made up of 
three elements, the fine sand, which is the most important, 
the coarse sand, which is desirable, and the dust or filler, 
which is absolutely necessary. The mineral aggregate 
of a standard mixture may, therefore, be considered from 
the following points of view. 

First point, 100- and 80-mesh sand 17 + 17 = 34 per cent. 

Second point, 10-, 20-, and 30-mesh sand 10+8 + 5 = 23 
Third point, Filler +2 00 sand. Dust+fine sand =17 

Or for the complete surface mixtures: 



70 



ASPHALT CONSTRUCTION 



First point, loo- and 8o-mesh sand 13 + 13 = 26 per cent. 

Second point, 10-, 20-, and 30-mesh sand 3 + 5+8 = 16 

Third point, filler+200 sand =13 

Fourth point, bitumen = 10. 5 

Or these points may be expressed in one of the following 
ways: 



Correct 
surface 
mixture, 
100% 



ASPHALT SURFACE MIXTURE 
Bitumen 



10.5% 
(4th point) 



Mineral ag- 
gregate, 

89.5% 
(ist point) 
(2d point) 
(3d point) 



Filler, 13.0% 
(3d point) 



Sand, 76.5% 
(ist point) 
(2d point) 



Mesh. 

100. 13.0 1 ^ ^ 

Q r 26.0% 

80.13.0 J 

(ist point) 

50 23.5% 

40 11.0% 

30. .8.0 ] 

20. .5.0 \ 16.0% 

10. .3.0 J 

(2d point) 



ASPHALT SURFACE MIXTURE 

Composition 

Bitumen 10.5 — 4th point 

Filler+200 sand 13.0 — 3d point 



Mineral 
aggre- 
gate, 
89.5% 




^ 

I 

n 



Correct 
asphalt 
mixture, 
100% 



I 



SURFACE MIXTURES 71 

The surface mixture, therefore, may be regarded: 
First, as a whole. 
Second, as a mixture of bitumen and a mineral 

aggregate. 
Third, as a mixture of bitumen, filler, and sand. 
Fourth, as a mixture of bitumen, filler, loo- and 80- 
mesh sand and 10-, 20-, and 30-mesh sand in 
suitable proportions. 
For example, take a New York mixture: 
First, New York mixture. 
Second, 10.5 per cent, bitumen, 89.5 per cent. 

mineral aggregate. 
Third, 10.5 per cent, bitumen, 13.0 per cent, dust, 

76.5 per cent. sand. 
Fourth, 

Bitumen 200 100 80 50 40 30 20 10 

Dust 

10.5 I3-0 26.0 23.5 II. o 16.0 

or 

10.5 13.0 13.0 13.0 23.5 II. o 8.0 5.0 3.0 

^'In forming an opinion, therefore, of an old or new 
surface mixture it becomes evident that the four points 
which have been described must be considered. These 
points may be differentiated from the composition of 
an old mixture or combined to form a new one. 

^^The primary consideration is the sand and the first 
point that it shall contain a normal and sufl&cient amount 
of 100- and 80-mesh material. This was, and undoubt- 
edly is to-day, the most essential feature in making a 
satisfactory mixture. It is essential because without 
this fine sand the mixture is porous and open, and more 
particularly because, unless it is present, a sufficient 



72 ASPHALT CONSTRUCTION 

amount of dust or filler cannot be used. The fine sand 
prevents the dust from balling up and making a lumpy 
mixture and, as will eventually appear, the larger the 
amount of fine sand the more dust can be introduced 
without difficulty. In the earlier mixtures, 1880 to 
1896, a large percentage of dust could seldom be used, 
although the attempt was often made, as the resulting 
mixture was difficult to handle and rake. 

" The second point or consideration lies also in the sand 
grading and is the regulation of the amount of the 10-, 
20-, and 30-mesh sand grains. In the Fifth Avenue 
mixture this material amounted to 16 per cent. It was 
unavoidable there, owing to the character of the sand 
available, but was beheved to be desirable in several 
ways. In the first place, it seemed to fill the place taken 
by broken stone iii hydraulic concrete, and to carry the 
traffic, so to speak. In the second place, it gave a less 
slippery surface than a finer mineral aggregate. In 
both these ways the coarse material is desirable, but 
closer study and experience has shown that at times 
it may be reduced or largely omitted to advantage, 
especially in damp climates. 

^^ To bring about a satisfactory arrangement of the first 
two points, or sand grading, one or more kinds of sand 
are necessary, usually more than one. For example, 
in the Fifth Avenue mixture the main sand supply was 
deficient in 100- and 80-mesh grains. It was, therefore, 
necessary to add a certain amount of fine sand consisting 
predominantly of grains of this size. 

'' The third point, and one also of great importance, is 
that the amount of filler or dust shall be sufficient. In 
the standard mixture of 1899 this was intended to reach, 
together with the small amount of 200-mesh sand and 



SURFACE MIXTURES 73 

the natural filler present in Trinidad asphalt, 13 per 
cent. In the older, coarse Washington and St. Louis 
mixtures of the early nineties the filler and 200 sand 
rarely reached 7 per cent., and in St. Louis fell, at times, 
below 3 per cent. This was attributable to two causes: 
one, the fact that such coarse mixtures would not carry 
much dust without balling, and the other, because it 
was considQred at that time uncertain if there was any 
merit in using a filler. We now know that dust gives 
stability to the mixture, aids in excluding water, and that 
the best surfaces are those which, up to a certain limit, 
contain the most filler. In the standard mixture of 
1899 the largest amount of dust which such a sand 
grading could carry was about 13 per cent., owing to the 
relatively small amount of 100 and 80 sand grains. 
Beyond this percentage the mixtures would become 
greasy or would ball. 

^^With the first three points arranged in a satisfactory 
way, the fourth or last point was to decide on how much 
asphalt cement the mineral aggregate would carry. This 
has been determined in recent years by the pat test 
which readily shows whether an excess or deficiency in 
asphalt cement has been used. This test cannot, in all 
probability, be improved upon. If each grain of material 
in the mineral aggregate is coated with asphalt cement 
and the voids more than filled the excess will be squeezed 
out in making a pat and stain the paper excessively. 
If the voids are not filled the only stain upon the paper 
will be a light one from the cement coating the grains of 
sand. A perfect mixture will contain just enough cement 
to fill the voids in the aggregate, stain the paper well but 
not excessively. The hotter the mixture the more liq- 
uid the asphalt cement and the freer the stain. Cold 



74 ASPHALT CONSTRUCTION 

mixtures will give no indication, while the difference in 
the markings of a fine and coarse sand will be readily 
learned by experience. 

'^The preceding instructions are satisfactory for turning 
out a mixture for the conditions ordinarily met with if 
the available materials admit of following them, or for 
judging the character of old surfaces when they have 
been resolved into their constituents by analytical 
methods." 

The pat paper test which is referred to above, is thus 
described in the author's book, ^^The Modern Asphalt 
Pavement." 

*^A small wooden paddle with a blade 3 to 4 in. wide, 5 or 
6 in, long, and 1/2 in. thick, tapered to an edge at one end 
and with a convenient handle at the other, is used to take as 
much of the hot mixture from the wagon as it will hold, being 
careful to avoid any of the last droppings from the mixer 
which may not be entirely representative of the average 
mixture. Samples of mixture should never be taken from 
the mixer itself, but only from the wagon after mixing is 
completed. 

^'In the meantime a piece of brown Manila paper with a 
fairly smooth surface, 10 or 12 in. wide, and torn off at the 
same length from a roll of this paper, which can be had at 
any paper warehouse, is creased down the middle and opened 
out on some very firm and smooth surface of wood, not stone 
or metal, which would conduct heat too rapidly. The hot 
mixture is dropped into the paper sic' e ways from the paddle 
and half of the paper doubled over on it. The mixture is 
then pressed down flat with a block of wood of convenient 
size until the surface is flat. It is then struck five or six 
sharp blows with the block, until the pat is about 1/2 in. 
thick." 

The paper will be found to be stained to a different 



SURFACE MIXTURES 



75 



degree depending upon whether there is a deficiency, a 
proper amount or an excess, present. Examples of such 
stains are illustrated in the accompanying Figs. A to D. 

In this way, the amount of asphalt cement in use in 
making a mixture, can be readily regulated, and the pat 
papers obtained will be evidence of the character of the 
mixture that is turned out. Where a laboratory exami- 
nation is to be undertaken, a sample of surface mixture 
which is made from the material compressed between the 
paper can be used for this purpose, trimming it down 
into the proper form and sending it, accompanied by the 
paper, for the purpose. 

Unfortunately at the present time the necessity for 
such control of asphalt surface mixtures as has been pre- 
viously described has not been universally recognized. 
During the years 191 1 and 191 2 mixtures which were 
laid in various parts of the United States have come 
under the observation of tie writer, some of which were 
far from satisfactory. As examples of poor work the 
following are illustrative: 



Bitumen 


200 


100 


80 


SO 


40 


30 


20 


10 


On 

10 


8.6 


9-4 


II. 


18.0 


31.0 


S-o 


9.0 


4.0 


3-0 


I.O 



Penetration, 68. 



This mixture laid in a northern city in 191 2, is made 
with a sand of very desirable grading, corresponding 
practically to the standard, but it is deficient in filler 



76 



ASPHALT CONSTRUCTION 



and, in consequence, does not carry enough bitumen. 
Of the components entering into the mixture but 8.2 
per cent, was dust, and it is probable that this was a 
coarse material, and at least half as much again should 
have been used. With a sufl&cient amount of filler the 
asphalt cement would be of suitable consistency for use 
in the cold climate where this pavement was laid, but 
with the absence of sufl&cient filler it would seem to be 
too soft. 

In a small southern city, in the same year, a surface 
mixture was laid, of which the extremes and average 
composition as regards percentage of bitumen were as 
follows : 



PASSING MESH 





Bitumen 


200 


100 


80 


50 


40 


30 


20 


10 


High 


13.0 


13.0 


6.0 


8.0 


27.0 


10. 


19.0 


3.0 


I.O 


Low 


9.9 


II. I 


4.0 


5.0 


23.0 


12.0 


23.0 


7.0 


5-0 


Average. . . 


II. 4 


12.6 


6.0 


6.0 


22.0 


II. 


21.0 


5-0 


4.0 





Penetration 




ligh 


Low 


Average 


92 


30 


55 



There is a great lack of uniformity in this mixture, 
both in percentage of bitumen and in its consistency, 
the variations being far greater than should occur in good 
practice. The amount of dust was only 60 lb. with 11 
cu. ft. of sand, which shows that there must have been 
a deficiency in filler, although the amount of material 




Light 

{Facing Page 76) 




Medium 




Strong 




Heavy 



SURFACE MIXTURES 



77 



passing a 200-mesh sieve appears to be sufficient. The 
sand grading shows a lack of particles of sizes passing 
the 80- and loo-mesh sieves and a large amount of 
coarse sand, but in a small city this is not a serious 
consideration if the mixture is satisfactory in other 
respects. 

In another northern city a mixture was laid which 
shows similar wide variations. 



PASSING MESH 



Bitumen 


200 100 


80 


SO 


40 


30 


20 


10 


On 

10 


II. 

8.2 


10. 
5-8 


12.0 

5-0 


12.0 


33.0 
52.0 


9.0 
6.0 


10. 
10. 


2.0 
4.0 


I.O 

3-0 


1 .0 



Penetration, 133-50. 

It will be seen that the sand grading in this town was 
not carefully regulated. It was at times good, as in 
the case of the mixture carrying 11 per cent, of bitumen, 
and at times very bad, as in the case of the mixture 
carrying 8.2 per cent, of bitumen. The percentage of 
filler was very deficient at times, which, with the sand 
grading accounts in part for the low bitumen, and at 
other times approaches a more satisfactory figure. The 
penetration of the asphalt cement varied^from 133 to 
50, which is unsatisfactory. 

In 191 1 a sheet asphalt pavement was laid in an Ohio 
town, the surface mixture for which carried 9.2, 9.3 and 
9.4 of bitumen in three cases, 11. 2 in two cases and 11.00 
in another. The amount of filler was usually deficient. 



78 



ASPHALT CONSTRUCTION 



running as low as 6.6, 6.9 and 7.0, and averaging about 
8 per cent. The following are data in regard to the 
extremes occurring in this town: 



PASSING MESH 



Bitumen 


200 


100 


80 


50 


40 


30 


20 


10 


On 

10 


II. 2 

9-2 


II. 8 
6.8 


6.0 

lO.O 


14.0 
14.0 


31.0 
36.0 


lO.O 

8.0 


10. 
12.0 


3-0 
2.0 


2.0 
2.0 


1 .0 



Here again we see that a deficiency of filler neces- 
sitates the use of a small amount of asphalt cement. 
The sand grading in this city was apparently satis- 
factory, and all that was needed to make a good mixture 
was the proper use of filler and asphalt cement. 

In a southern city in 191 1 a surface mixture was turned 
out having wide variation in its composition, as shown 
from the following data: 







PASSING MESH 








, 1 


Bitumen 


200 


100 


80 


SO 


40 


30 


20 


ID 


II .2 

8-5 


12.8 

10. 5 


lO.O 
12.0 


12.0 
13.0 


29.0 
30.0 


8.0 
8.0 


14.0 
14.0 


2.0 
30 


I.O 
I .0 



These mixtures are made with a most satisfactory sand. 
The percentage of filler seems to be satisfactory, as over 



SURFACE MIXTURES 79 

lo per cent, usually passes the 200-mesh screen but, on 
reference to the proportions used in the mixture, it 
appears that only 80 lb. of dust were used for .a 9 cu. ft. 
box which, of course, with Bermudez asphalt, is too 
little, showing that much of the 200-mesh material must 
be sand and not serviceable as a filler. The percentage 
of bitumen shows wide variations, and is usually lower 
where the percentage of filler is low. The consistency 
of the asphalt cement is, in the opinion of the writer, too 
hard, varying from 28 to 40, even for a southern city, 
at least, if sufficient filler is used in the mixture. 

The facts which have been given in regard to inferior 
mixtures show the necessity of more careful attention 
to the principles which have been laid down in the 
preceding pages, and point to the conclusion that greater 
carelessness exists to-day jthan should be the case. It 
cannot be considered, however, that much of the work 
which has been done within the last few years will prove 
to be an immediate failure, but it can be confidently 
asserted that mixtures of the type which have been laid 
in many instances in 1911 and 1912, will prove to be 
short-lived as compared to those constructed on rational 
principles and on lines which have given the best results 
under trying conditions, that is to say they will prove 
to be pavements which will last not fifteen years, but 
only ten or even five years, and it is with a view to cor- 
recting these mistakes that this book has been prepared, 
as well as to call attention again to the principles which 
were laid down at considerably greater length in the 
writer's original publication, ''The Modern Asphalt 
Pavement.'' 

Density of Sheet Asphalt Surfaces. — ^The density of a 
sheet asphalt surface is an important consideration in 



80 ASPHALT CONSTRUCTION 

determining its character, and its behavior in the 
laboratory, under impact when compressed is a valuable 
means of judging the quality of the binding material and 
the capacity of a pavement made with such a mixture 
to resist the impact of the horse's hoof and travel in 
general. A surface mixture when heated can be com- 
pressed in a steel cylinder in the laboratory under the 
impact of a hammer or falling weight, and it will be found 
that the density of the best mixtures, thus compacted, 
will be, where ordinary limestone is used as a filler from 
2.22 to 2.25, and 2.27 when made with Portland cement. 
The calculated density of such mixtures is only about 
two units higher in the second place of decimals, than 
when laid on the street and thoroughly rolled, so that 
they contain practically no voids. In many inferior 
mixtures which have not given satisfaction, the density, 
as taken from the street surface, is found to be low, from 
2.00 to 1.86. The character of a mixture can, therefore, 
not only be determined by observing its density in the 
laboratory but also from the density which it attains in 
the street under travel. 

By means of an instrument designed by Mr. Logan 
Waller Page, Director of the Office of Public Roads, 
U. S. Department of Agriculture, the resistance to 
impact of cylinders of the form which has been described, 
may be determined and valuable data obtained for the 
differentiation of different types of mixtures. In making 
these tests the cylinders afe 1.25 in. in diameter and i 
in. high and weigh about 50 grm. They are firmly 
held beneath a plunger resting on the surface of a 
spherical bearing having a radius of 0.4 in. A weight of 
2 kg. is then allowed to drop from the distance of i cm. 
This is increased i cm. at each blow until the test piece 



SURFACE MIXTURES 81 

breaks. The number of blows it will withstand has been 
found to be dependent upon: 

1. The sand grading. 

2. The character of the sand. 

3. The amount of filler present. 

4. The character of the asphalt in use. 

5. The consistency of the asphalt cementing material 
and the temperature at which the tests are made. 

6. The density and degree of compaction of the test 
piece. 

7. The percentage of bitumen in the mixture. 

Some results of such tests are presented in the 
accompanying table taken from '^The Modern Asphalt 
Pavement," and are instructive. 

The tabulated data demonstrate that surface mixtures 
made with Trinidad asphalt are superior to any others if 
properly proportioned, and that the most desirable are 
those the mineral aggregate of which is. fine, or contains 
a high percentage of bitumen and filler. In fact, the char- 
acter of the mineral aggregate and the percentage of 
bitumen have an important influence on the behavior 
of the mixture under impact. Data obtained at different 
temperatures show that the mixtures in which Trinidad 
lake asphalt is the cementing material are more resistant 
to impact at extremes of temperature than where the 
binding material is some other form of asphalt. 

Resistance to A ction of Water. — The ability of a mixture 
designed on rational principles to resist the action of 
water has been noted. The denser the mixture and the 
larger the percentage of bitumen which it contains, the 
more resistant the surface will be to water action, and 
the more suitable such mixtures will be to meet un- 
favorable conditions of this description. 



82 



ASPHALT CONSTRUCTION 



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SURFACE MIXTURES 



83 



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84 



ASPHALT CONSTRUCTION 



This is well illustrated by the amount of water absorbed 
at different periods by the old and coarse Washing- 
ton mixtures of 1893 as compared to the improved type 
laid at the present time, as shown in the following 
table: 



ABSORPTION OF WATER BY CYLINDERS OF ASPHALT SURFACE 
IN POUNDS PER SQUARE YARD 





Washington, 1893 


Standard mixture, 
1906 




Trinidad 


Bermu- 
dez 


Trinidad 


Bermu- 
dez 


7 days 

14 days 

28 days 


0.314 
0.434 
0.502 


0.063 

0.194 
0.306 


0.080 
0.093 
0.107 


0.094 
0.093 
0.104 



All of the preceding facts point to the necessity of 
selecting asphalt of the highest quality, a careful regu- 
lation of the character of the sand, the amount of filler 
and the percentage of bitumen in use in the construction 
of a durable sheet asphalt surface. 

An appreciation of the necessity for the precautions 
which have been insisted upon in this chapter is well 
realized by some contractors. As illustrating this a 
circular of instructions has been issued by the chemist of 
a corporation^ who is engaged in the supervision of sheet 
asphalt work, who has followed the principles which the 

^ American Asphaltum & Rubber Co. 



SURFACE MIXTURES 85 

writer has laid down in previous publications, and which 
reads as follows : 

"LABORATORY RULES AND INSTRUCTIONS FOR PLANT 
FOREMEN AND CHEMISTS" 

^'i. No sand shall be hauled on the job unless it has been 
previously O. K'd. by main laboratory. 

^^2. The chemist testing the sand or sands shall go to the 
pit or other source of supply and take representative samples, 
test them and make a report of test to main laboratory. 
A I lb. sample of each sand so tested shall be sent to 
laboratory. 

*^ (a) Should it be necessary to use more than one grade of 
sand a report of the test of the proposed mixture, together 
with a I lb. sample of this mixture, shall be sent to main 
laboratory. 

^'(b) Chemists in making a preliminary report of suitable 
sand should state kind of sand (lake, river, or bank), avail- 
able quantities, accessibility to railroad, or distance of haul 
to plant, price per cubic yard (f.o.b. source of supply or 
plant) and general appearance and character of sand, i.e., 
whether it contains clay, loam or other impurities. 

'^ (c) In selecting a suitable sand for paving work, chemist 
should look for a clean moderate sharp sand having a grading 
that comes within the limits given below. In case more 
than one sand must be used to get the desired grading, chem- 
ist must state in what proportions different sands must be 
mixed. 

"(^) Chemist in selecting a suitable sand must select a 
sand that will not vary more than 5 per cent, from the fol- 
lowing gradings, i.e., 5 per cent, for the three combined 
gradings. 

" (e) Should it happen that no suitable sand coming within 
above limits is found available, a special report on available 
sand should be sent to main laboratory.'' 



86 



ASPHALT CONSTRUCTION 

STANDARD GRADINGS 



Mesh 



Heavy traffic, 
per cent. 



Light traffic, 
per cent. 



Passing 200 
Passing 100 
Passing 80 
Passing 50 
Passing 40 
Passing 30 
Passing 20 
Passing 10 




3. Oil 

"Upon arrival of each car of fluxing oil, plant chemist or 
foreman shall send in a i pt. sample of same to main 
laboratory. 

4. Samples 

"On first day^s run of top mixture a i lb. representative 
sample of drum sand, filler (limestone dust or Portland 
cement) asphaltic cement and refined asphalt shall be sent 
to main laboratory. 

"(a) During first week of each month a set of samples 
similar to above shall be sent to main laboratory. 

"(6) Should there be a noticeable change in any of the 
above materials during the month a sample of same with 
accompanying report should be sent to main laboratory. 

" (c) Should it happen that job does not last for a month, 
two sets of above samples must be sent in, one set on first 
day's run of top and the second a few days before completion 
of work.'' 



SURFACE MIXTURES 87 

5. Pavement Samples 

A sample 12X12 in. from each street of finished pavement, 

carefully cut and neatly packed and labeled with form No 

should be sent by freight to main laboratory. 

*^ (a) Should any street contain over 10,000 sq. yd. a sample 
similar to above should be sent in for each 10,000 sq. yd. 

^\h) If more than four pavement samples are to be sent 
in it will not be necessary to send in sample from any street 
having a yardage of less than 2,000 sq. yd. 

^^ (o) Should there be any noticeable change in mix, or 
materials entering into mix, a pavement sample of each 
different niixture should be sent in. 

6. Progress Maps 

"A weekly progress map properly filled out must be sent 
to main laboratory each week.'' 

7. Penetrations and Mixture 

'^ Plant chemist or foreman must get penetration limits and 
proposed mix from main laboratory before starting work. 

^'(a) Plant chemist or foreman may make any small 
changes in mix which he thinks advisable, but any such 
changes must be immediately reported to main laboratory, 
giving full information and reasons for making change.'' 

8. Daily Work 

"Blank form No shall be carefully and completely 

filled out each day by plant chemist or foreman. 

" (a) On first report of top mixture the weight of one cu. 
ft. of drum sand should be noted. 

" {h) If binder and top are run the same day separate re- 
ports should be made." 

9. Binder Work 

"When running binder, a 2-oz. representative sample of 
asphaltic cement from each kettle should be taken and label 



88 ASPHALT CONSTRUCTION 

No filled out and sent with the sample to main labo- 
ratory.'' 

lo. Top Work 

''When running top, the following samples should be taken 
and sent to the main laboratory: 

" (a) One 2-oz. sample of A. C. from each tank used. 

'' (b) One representative pat sample from mixture at plant. 

" (c) One small sample of mixture taken from street. 

*' (d) Proper labels for above samples should be made out 
and sent in with report No 

"(^) Samples should be so numbered that proper labels 
can be put on the right samples upon their arrival at the main 
laboratory.'' 

II. Drum Sand 
"Plant chemist or foreman should test drum sand grading 
at least once each day and as many more times as is necessary 
to keep a uniform grading. A report of each day's sand 

grading shall be made out on blank No and sent to main 

laboratory." 

12. Plant Chemists 

"If there is a plant chemist on the job he is to have complete 
charge of mix but at all times must co-operate with the plant 
foreman." 

13. Estimates 

"After mix has been regulated plant chemist must estimate 
quantities of materials required to complete work and make 
written report of same to superintendent, sending copy of 
this report to main laboratory and copy to manager of 
construction." 



14. INFORMATION 

'A copy of any information regarding mixture given to 
/ city official must be sent to main laboratory and such 



SURFACE MIXTURES 89 

information must not be given without first advising main 
laboratory that it has been requested." 



GENERAL INFORMATION FOR PLANT CHEMISTS 
AND FOREMEN 

"It is the policy of this company in its paving work to 
combine quality with quantity, in fact put quality above 
everything, and in recognition of this fact we respectfully 
ask that plant foremen and chemists co-operate in every 
possible way in putting out a most uniform and high-class 
mixture. 

"It is at the paving plant that the pavement is made and 
it is here that the qualities of the asphalt and other materials 
and the reputation of the contractor is at stake, and it is 
only by the fullest co-operation and harmony between every 
one connected with the plant that the best results can be 
obtained. 

"The following points should be noted and carried out as 
near as possible by plant foremen and chemists with the 
view of obtaining the best results. 

"i. Top mixture should have at least fifteen seconds dry 
mix and from forty-five seconds to one minute wet mix. 

"2. A. C. scales should be checked and rebalanced every 
hour, or more often if mixture does not look uniform. Scales 
should be cleaned every day. 

"3. Sand scales should be checked every day and cleaned 
at least once every week. 

"4. Tanks should be cleaned every week, or more often, 
if using Trinidad or Bermudez Asphalt and direct heat. 

"5. In using "Pioneer" asphalt the temperature of the 
mix should be kept as near 300° F. as possible during the sum- 
mer and about 325° F. during the spring and fall months. 

"6. Temperature of asphaltic cement in kettles shall not 
exceed 340° F. unless special instructions are issued from main 
laboratory. 



90 ASPHALT CONSTRUCTION 

"7. Any material over 380° F. or below 240° F. should be 
rejected. 

"8. Binder should go out at a temperature of about 275° 
F. and any over 340° F. should be rejected. 

^^9. Temperatures and limits on other asphalts will be 
given before starting work.'' 

H. D. PULLAR, 

Chemist, 

The above circular shows the realization of the neces- 
sity of closely regulating plant work, and the sugges- 
tions which it contains can be followed with advantage 
by any contractor or his employees. 

Grit Mixtures. — Something has been said of this type 
of mixture in discussing the mineral aggregate. In 
the form of asphalt blocks it has been extensively used 
but, owing to the fact that the asphalt cementing 
material in that case must be made undesirably hard 
in order to permit of the transportation of the blocks 
from the point of manufacture to another where they 
are laid without losing shape, it is not one that has 
proved satisfactory under heavy travel. When used 
in the monolithic form and hot, a grit mixture, 
the cement under these circumstances being of the 
consistency employed in ordinary sheet asphalt surfaces, 
is very satisfactory and has proved successful, especially 
in Buffalo and Rochester, N. Y., for many years. Con- 
structed under the so-called Topeka specifications it 
will, in the opinion of the writer, prove a failure, as is 
evident from the following facts which have been stated 
in an article contributed to the Engineering Record of 
June 29, 1912. 

"The bituminous mixture used in the manufacture of 
asphalt block would fall, in composition, practically 



SURFACE MIXTURES 



91 



if not exactly, within the limits in percentage of bitu- 
men and of the various sized particles of the mineral 
aggregate provided for in Judge Pollock's ruling. Natu- 
rally an asphalt block could not infringe the Warren 
patent, as it has been in use for many decades. The 
composition and grading of the mineral aggregate of 
the average asphalt block and of the finer material of 
which it consists, when calculated to loo per cent., 
with the exclusion of the fine stone, is represented by 
the following figures: 



Bitumen 

Passing 200 mesh. . . 
Passing 80 mesh. . . 
Passing 40 mesh... 
Passing 10 mesh... 
On 10 mesh 35.5 



Block as made 


Stone out 


7.0 
14.0 

8.0I 
7.0 

28. 5 

35-5 


15.0 


10.9 
20.7 
12.4 

10. J 
44.2 





100.00 




100.00 



*^ Using the extremes of composition within the limits 
specified by Judge Pollock, mixtures of two types may 
be made, one low in bitumen and high in coarse material, 
and the other rich in bitumen and TOth a minimum 
amount of coarse material. These types of mixtures 
and the character of the fine material which they contain, 
with the fine stone excluded, are as follows: 



92 



ASPHALT CONSTRUCTION 



Bitumen 7.0 

Passing 200 mesh 5.0 

Passing 80 mesh. ...... 18.0 

Passing 40 mesh . 38.0 

Passing 10 mesh 22.0 

On 10 mesh 10. o 



10 

7 
26 

55 



II. o 
II. o 

30.0 

33-0 
10. o 

5.0 



12 
12 

35 
38 



100. o 100. o 100. o 100. o 

''The satisfactory nature of a mixture containing fine 
stone is no greater than that of the finer portion or mor- 
tar, when the latter is looked at as an ordinary sheet 
asphalt surface. The composition of the sheet asphalt 
mixture now in use in the Borough of Manhattan is as fol- 
lows and, although it is not an ideal mixture, being defi- 
cient in fine sand, it will serve as a basis of comparison: 



Bitumen 10.8 

Passing 200 mesh 12.2 

Passing 100 mesh 5.0 

Passing 80 mesh. 8.0 

50 mesh 37.0 

40 mesh 9.0 

30 mesh 13.0 

20 mesh 3.0 

10 mesh 2.0 



Passing 
Passing 
Passing 
Passing 
Passing 



lOO.O 



10.8 
12.2 

59-0 
18.0 

lOO.O 



"It is very evident from the preceding data that the 
grading of the finer part of the Topeka mixture is very 
unsatisfactory, that is to say, it would make a poor 
sheet asphalt pavement, and for the same reason an 
unsatisfactory surface even after the addition of fine 
stone. The limits prescribed by Judge Pollock neces- 
sitate the use of a mineral aggregate containing less than 



SURFACE MIXTURES 



93 



30 per cent, of fine sand which will pass a 40-mesh screen, 
and from 25 to 55 per cent, of concrete sand retained 
on a 40-mesh screen and passing one of 10 meshes to the 
inch. Both of these requirements necessitate the omis- 
sion of an amount of fine sand particles which is well 
known to be desirable and necessary in a satisfactory 
asphalt surface mixture, and the use of much too large 
a percentage of concrete sand of 10, 20 and 30 mesh size, 
which are well known to cause scaling of an asphalt 
surface when in excess." 

^^A so-called Topeka mixture has recently been laid in 
the neighborhood of New York City which has the follow- 
ing composition, complying with the terms of the ruling: 





Specifica- 
tion 
limits 


Topeka 

mixture 

laid 


Calcu- 
lated 
with 
stone 
out 


Bitumen 


7-1 1 

5-1 1 
18-30 

25-55 
8-22 
-10 


8.00 

6.25 

22.7s 

46.50 

12.75 

3-75 


9.6 

7-5 

27.2 

55-7 


Passing 200 mesh 

Passing 40 mesh 

Passing 10 mesh 

Passing 4 mesh 


Passing 2 mesh 









'^The finer portion of the mixture, from which the stone 
of pea size has been removed, if calculated to 100 per 
cent, will be found to consist of over half concrete sand, 
and to be very deficient in fine sand. It is not a well 
balanced mixture." 



94 



ASPHALT CONSTRUCTION 



"A surface which would be infinitely superior to that 
provided by the Topeka ruling would be one which 
would consist of a standard sheet asphalt surface mixture 
to which 20 to 30 per cent, of fine stone, such as is used 
in the manufacture of asphalt blocks, and less than 10 
per cent, of the small material which will pass a 2-mesh 
screen, has been added." 

Such surface mixtures have been in use for a great 
many years, and below are given the proportions and 
analysis, with grading, of one used in the Borough of 
Manhattan, in the City of New York, in 1904, and in 
Buffalo, N. Y. in 1911, and before that for many years: 





New York 


Buffalo 


Grit 


56s lb. 
475 lb. 
150 lb. 




Sand 




Dust 




A. C 


130 lb. 










1320 


Bitumen 


7-2% 


9.9 


Passing 200 mesh 


12.8 


8.1 


Passing 100 mesh 


6.0 


7.0 


Passing 80 mesh 


5-0 


20.0 


Passing 50 mesh 


II. 


26.0 


Passing 40 mesh 


6.0 


2.0 


Passing 30 mesh 


S-o 


I.O 


Passing 20 mesh 


S-o 


I.O 


Passing 10 mesh 


6.0 


3-0 


Retained 10 mesh 


36.0 
100. 


22.0 




lOO.O 



SURFACE MIXTURES 95 

Of course in addition to the amount of asphalt cement 
required by that portion of the mineral aggregate repre- 
senting the sheet asphalt mixture, enough must be 
used in addition to coat the surface of the stone which 
is present. 

It appears that the density of a well-compressed sheet 
asphalt surface is 2.2, or slightly more than this. As the 
grit mixture carries a considerable percentage of stone 
and a smaller percentage of bitumen, its density will be 
considerably greater when compressed. In an asphalt 
block, the entire mineral aggregate of which consists of 
crushed trap-rock, a material of high specific gravity, the 
density is about 2.5. In a grit mixture, the finer portion 
of the aggregate of which consists of sand with a lower 
specific gra^dty than trap-rock, the density would be 
lower, but it should reach at least 2.35 when com- 
pressed. 

Instead of the crushed rock, suitable gravel may be 
used, but the rounded form of the particles of gravel 
and their very smooth surface, do not make a mixture 
which is as satisfactory under heavy travel, as that in 
which crushed rock is used. The rounded particles of 
gravel are more easily torn out of the surface under 
travel than fragments of stone. It is, nevertheless, 
an extremely valuable form of surface where horse- 
drawn vehicles form but a small portion of the travel, 
and will, no doubt, meet with success under proper 
conditions. 

Asphaltic Concrete Surfaces. — A concrete consists for 
the largest part of broken stone, either of uniform or 
graded sizes, the voids in which are filled with a mortar, a 
Portland cement mortar in the case of hydraulic concrete, 
and an asphaltic mortar in the case of asphaltic concrete. 



96 



ASPHALT CONSTRUCTION 



Material of this t3^e has been used in the construction of 
paving surfaces since the early seventies of the last 
century, although it was not done at that time on a 
rational basis. The Evans pavement laid in Washington, 
D. C, in 1873 had the following composition: 





Entire 


Mineral 






pavement 


aggregate 




Bituminous matter soluble in CS2 (T28) 


3.0% 










Mineral matter passing 200-mesh 


3.2 




3.4% 


3- 


4 


screen. 












Mineral matter passing lo-mesh 


37.1 


37.1 


38.2 


38 


2 


screen. 












Mineral matter passing 8-mesh screen. 


2.7 




2.8 






Mineral matter passing 1/4-in. screen. 


10.5 


13-2 


10.8 


13 


6 


Mineral matter passing 1/2-in. screen. 


14.3 




14.7 






Mineral matter passing 3/4-in. screen. 


14.7 




15.2 






Mineral matter passing i-in. screen. . . 


14.5 


43-5 


14.9 
100. 


44 


8 




100. 





The above data show that the Evans surface consisted 
of 58 per cent, of stone in size varying from 1/4-in. to 
I -in. material, the voids in which were filled with a tar 
mortar. This is plainly a true concrete. Asphaltic con- 
crete, as far as the writer is aware, was first produced in 
1896, and laid as a sidewalk in Long Island City, N. Y. 
It had the following composition: 



SURFACE MIXTURES 97 

Test number 82,157 

Bitumen 7-3% 

Passing 200-mesh screen 8.2 8.2 

Passing lo-mesh screen. ... 24.2 
Passing 8-mesh screen .... 1.2 

Passing 1/4-in. screen 7.9 9.1 

Passing 1/2-in. screen 30.9 

Passing i-in. screen 20.3 

Retained i-in. screen. ..... .0 51 . 2 

100. o 
Voids in mineral aggregate. . 15.5% 
Later on a similar mixture was laid as a street surface 
in Muskegon, Michigan, which had the following com- 
position: 

Test number 81,117 

Bitumen 7-4% 

Passing 200-mesh screen. ... 7.4 7.4 

Passing lo-mesh screen. ... 34.0 34.0 

Passing 8-mesh screen .... 2.8 

Passing 1/4-in. screen 1 1 . 2 14.0 

Passing 1/2-in. screen 18.0 

Passing i-in. screen 19. 2 37. 2 

, Retained i-in. screen .0 

100.0 

Voids in mineral aggregate 16.8% 

The mixtures cited give a very good insight into the 
character of the grading of the mineral aggregate and 
composition of such a mixture as it should be turned out 
to-day. It is unnecessary to enter here into a discus- 
sion of the infringement of certain patent rights by such 
mixtures, as this is not a subject for the engineer to pass 
7 



98 ASPHALT CONSTRUCTION \ 

upon, and lies wholly with the courts and with the inter- i 
pretation of the law. Such concrete surfaces are un- j 
doubtedly very satisfactory for light horse-drawn travel '\ 
and for motor travel of any description, when a standard ! 
asphalt is used as a binding material. \ 

In a previous chapter on Broken Stone, the character ] 
of the material suitable for use in asphaltic concrete has 
been discussed. It should be a trap-rock or hard lime- 
stone, but preferably the latter, as there is better adhe- 
sion of the asphaltic cement to the granular fracture of 
hard limestone than to the glassy surface of trap-rock. 

The manner of assembling the mineral aggregate for 
the asphaltic concrete is discussed at length under the 
heading. Close Binder, in a previous chapter. j 

In regard to regulating the percentage of asphaltic 
cement in use in asphaltic concrete, this, of course, can-^ 
not be done with the pat paper, as in the case of a sheet -^ 
asphalt surface mixture composed of sand alone. It 
must be done by eye and with the use of good judgment. 
Whether the amount is correct, can be best determined 
by the appearance of the material in the truck, after the 
haul from the plant to the street. Where it is to be used 
as a surface to carry travel it should have settled into a 
compact mass, the top of which should show a slight 
excess of bitumen as a rich coating, whereas if it is in- 
tended for a binder course no excess of bitumen should 
appear and there should be some evidence of the coarser 
fragments of stone on the surface. An asphaltic con- ' 
Crete cannot be expected to have the bright and glossy 
appearance of clean stone coated with asphalt, as in 
the case of open binder, owing to the presence of sand. 

In the preparation of asphaltic concrete the asphalt 
cement in use should be much softer than that employed I 



SURFACE MIXTURES 99 

in the ordinary sheet asphalt surface mixture consisting 
of sand alone. It should not be harder than the consist- 
ency represented by 80 or 90 points on the penetration 
machine. 

Asphaltic Broken Stone Surfaces or Asphalt Maca- 
dam. — Experience having demonstrated that the ordi- 
nary water-bound broken-stone road will not meet the 
demands of travel which consists largely of motor vehi- 
cles, it has been generally recognized that some form of 
bituminous material must be used as a cementing material 
with broken stone to produce a surface which will re- 
sist travel of this kind. The inference can be readily 
drawn that the native asphalts which have been used 
successfully in sheet asphalt pavements would prove to 
be the most desirable material for the purpose, and this 
has been found to be the case in comparison with other 
materials, such as coal tar and the residuals of petroleum. 
It is undoubtedly due to the greater stability of the native 
asphalts under the conditions which are to be met. 

Bituminous broken-stone surfaces are constructed by 
either the so-called penetration or by the mixing process. 
The asphaltic cement is not however used in the same 
way in both, although the character of the material 
should be quite the same. 

In the penetration process the stone is placed in the 
road in the manner that it would be if a water-bound 
broken-stone road was to be constructed, and the asphalt 
cement is applied to it in the amount decided upon, as 
uniformly as possible. This may be done after the stone 
is thoroughly compressed under the roller, or it may be 
partially compressed, the asphalt cement then appHed, 
and final rolling completed, as may be considered most 
desirable. 



100 ASPHALT CONSTRUCTION 

Assuming that Bermudez asphalt cement is the binding 
material to be employed, the way in which it is melted 
alongside the road and the temperature at which it is 
maintained has a very considerable bearing on the 
success of the work. It can readily be too hot or too 
cold. If it is too cold it does not penetrate into the 
surface nor properly coat the stone. If it is too hot it 
forms too thin a layer upon the stone and runs through 
the voids to a position which is not near enough to the 
surface of the road. It is very important, therefore, 
that the temperature of the asphalt cement or road binder 
should be carefully regulated with thermometers. It 
should never be heated above 375° F. for two reasons; 
the road binder may be injured thereby and is, under any 
circumstances, hardened rapidly at high temperatures 
and, for the reason given above, it may be too liquid. 
It should not fall below 340° F. and not as low as that 
in extremely cold weather. The temperature must be 
regulated to a certain extent according to atmospheric 
conditions. 

The melting and maintenance of a bituminous road 
binder at the proper temperature will be very much 
influenced by the size and form of the kettles or melting 
tanks in which it is done. The material will be much 
more apt to be overheated in a small melting tank than 
in one of large size. It is recommended, therefore, that 
tanks of as large size as can be moved from place to place 
be used for this purpose. Agitation of some form should 
always be provided in order that the bitumen which 
comes in contact with the sides of the melting tank 
where they are exposed to the fire may have a proper 
circulation, and not be injured by remaining in contact 
therewith for a long time. Tanks should be available in 



SURFACE MIXTURES 101 

such numbers that a new lot of material may be melted 
and brought to the proper temperature before that in 
another kettle is exhausted. It is not good practice to 
add cold material to the melted supply which is being 
used on the road. 

The distribution of the road binder may be accom- 
plished by hand labor or by mechanical distributors. 
For distribution by hand various types of so-called 
pouring pots are available. Uniformity of distribution 
is dependent upon the skill of the man handling the pot. 
Pots with a broad horizontal orifice from which the 
asphalt runs in a regular stream upon the stone while 
the man walks backward without changing the position 
of the pot, apparently, do the most satisfactory work. 
Pots with narrower orifices, both vertical and horizontal, 
which require swinging the pot from side to side as the 
laborer retreats from the finished portion, are also in use. 
Uniform work has been done with these pots but they 
require more skill to manipulate. 

Mechanical devices for the distribution of hot road 
binder are numerous, but there are but few of them which 
are suitable for distributing asphalt cements or binders 
made from the native asphalts owing to the higher 
temperature at which they must be maintained, and 
their greater viscosity. The material distributed from 
the nozzles of these appliances may be in the form of a 
continuous current or a spray of atomized material. At 
present it would be impossible to say which produces the 
best result with the road binders composed of native 
asphalts. 

After the road binder has been applied to the stone it 
is further compressed, if the final compression was not 
originally applied. If this had taken place before the 



102 ASPHALT CONSTRUCTION 

asphaltic binder was added, broken stones or fragments, 
which are known as pea grit and which consist of par- 
ticles passing a screen with circular openings 5/8 in. in 
diameter, although coarser material is frequently used, 
are spread in sufficient quantity to fill the voids in the 
crushed stone which constitutes the surface. It is well 
swept and rolled in. Afterward the excess is removed 
and another coat of bitumen is applied to seal the sur- 
face. On completion of this application a further 
course of grit, sand or dust, often that which has been 
previously removed from the road, is spread to correct 
the stickiness of the surface, and the road is ready for 
use. 

The amount of a road binder made from Bermudez 
asphalt which is applied to the broken stone should be 
a gallon and a half in case the surface course is 3 in. 
thick, and somewhat less if it is made of smaller 
stone and is only 2 in. thick. In the first case the stone 
may be of i 1/2-in. size, but in the lesser thickness it 
should be of the size of binder stone — less than an inch 
in diameter. The seal or grit coat should amount to 
something more than half a gallon per square yard of 
surface, and less than three-quarters. These quantities 
apply solely to the use of the viscous, oily, stable lake 
asphalt binder, and would prove too large, owing to the 
bleeding which would arise under the temperature pro- 
duced by a summer's sun, for other materials derived 
from petroleum. 

When the asphaltic broken-stone road is constructed by 
the mixing process the material is turned out in the same 
manner as would be the case if it were an open binder, 
and the same precautions must be used in doing so. 
As has been previously said, the danger lies in having the 



SURFACE MIXTURES 103 

stone too hot, when it will retain an insufficient coating 
of the road binder, or too cold when it will retain too 
much. The difficulty with the mixing process is that the 
plants available for heating the stone do it in such an ir- 
regular way and with such variations in temperature, that 
a satisfactory result is not obtained. This is particularly 
true of methods of heating the stone alongside the road 
in portable mixers, and the best work is only accomplished 
where a large semi-portable plant is available for the 
purpose. After spreading and placing the coated stone 
in position in the road it is compressed like a binder course 
and the pea-grit fragments and seal coat completed in the 
same manner as for work done by the penetration method. 

Many excellent and many very poor pieces of construc- 
tion have been done by both the penetration and the mix- 
ing method, and it is evident that the character of the 
surface which is constructed will depend entirely on the 
care with which the work is regulated, particularly the 
temperature of the stone in the mixing process and of 
the asphaltic road binder in both methods. Attention 
to detail in these directions is as necessary as in con- 
structing sheet asphalt surface mixtures, and good re- 
sults cannot be expected otherwise. 

Asphalt Surface or Carpet Coats. — It has been a 
common practice for some time in Great Britain and on 
the Continent, to make an application of coal tar in its 
various forms to old road surfaces to mitigate or remove 
the dust nuisance, or to protect them from wear and 
disintegration. In America, where asphaltic materials, 
which are of a more suitable nature, are available, at- 
tempts have been made to use materials of this descrip- 
tion for the purpose, with the idea that such applications 
would be more lasting than the very temporary benefits 



104 ASPHALT CONSTRUCTION 

derived from the use of tar. It was readily recognized on 
careful consideration and also demonstrated by service 
tests that asphaltic oils and residuals which contained a 
considerable percentage of paraffine hydrocarbons do not 
have sufficient adhesive and binding qualities to permit 
of their successful use. This excludes the possibility 
of satisfactorily using in the East, materials derived from 
petroleum found in most of the fields in the United 
States, supplies of which are available^ at a reasonable 
price. The asphaltic oils are preferable for this purpose 
and alone give satisfactory results. These asphaltic 
oils are found in California, in Mexico and in Trinidad. 
The California oils are excluded from use in the eastern 
parts of the United States on account of the cost of 
transportation. The Mexican and Trinidad oils are 
available at reasonable prices. The oils, although both 
of an asphaltic nature, are of two different types. They 
are both sulphur oils, and from analogy would be looked 
upon as closely related to the native asphalts. The sul- 
phur in the Mexican, however, is in a different state of 
combination from that in the Trinidad oil and the man- 
ipulation of the Mexican material, on distillation, difficult 
on this account. The Mexican oil also carries from i to 3 
per cent, of hard paraffine scale pointing to the fact that 
the material is not entirely asphaltic and, therefore, not 
as satisfactory as the oil from Trinidad. Service tests, 
during the short time that they have been conducted, 
justify the conclusion that the Trinidad oil is the more 
satisfactory for the production of a surface coat on an 
old broken-stone or gravel road, or in a new gravel 
surface. 

Whatever the material which may be used for a carpet 
coat, it should be applied with a mechanical distributor 



SURFACE MIXTURES 105 

capable of handling it in a heated condition, preferably 
under pressure and either atomized or not. 

The life which a carpet coat may be expected to have 
will be dependent as well on the character of the surface 
to which it is applied and the manner of application, as 
upon the kind of material. A smooth water-bound 
broken-stone surface is the most desirable one, and a 
carpet coat should be made to adhere to this satisfac- 
torily if it is freed absolutely from dust and the oil 
applied at a high enough temperature in dry and warm 
sunny wxather. If, however, this is not the case, it will 
be necessary to make an application of naphtha or 
kerosene to obtain proper adhesion of the carpet. Most 
of the unsatisfactory carpet coats may be attributed to 
the fact that the bituminous material is not applied in 
such a way as to permit of thorough adhesion. There 
is no greater enemy to proper adhesion than dust of any 
description. In the asphalt industry, adhesion of 
asphalt to packages in which the refined material is 
contained, is prevented by claying the surface of the 
package, and the same result will be found if the surface 
of a road is dusty. This applies as well to a hydraulic 
cement concrete surface as to broken stone or other form 
of road. 

Where the dust cannot be thoroughly removed from 
the road surface for any reason, it is better to sprinkle 
it lightly with water before applying the bitumen, rather 
than to attempt to cover a dusty surface, as the dust and 
water will emulsify with the oil and adhesion will be ob- 
tained when the water dries out. This method of 
procedure is not alw^ays successful and can hardly be 
recommended as a substitute for thoroughly cleaning the 
road. 



106 ASPHALT CONSTRUCTION 

The amount of oil per square yard of surface should 
be half a gallon or slightly more than that, depending 
upon the smoothness of the surface. Regulation of the 
exact amount must be arrived at by good judgment and 
experience. 

After the application of the bituminous material coarse 
sand or fine grit or gravel should be sprinkled and rolled. 
Fine sand is most undesirable for this purpose as it 
readily displaces under travel, and causes a wavy surface. 
The same result is brought about by the use of sand to 
absorb superfluous bitumen which is softened by the 
summer sun. A final treatment of this description is 
of very great importance if a lasting and satisfactory 
carpet is to be obtained. 

The age of carpet coats will depend very much on the 
amount and character of the travel to which they are 
subjected. They are very satisfactory with motor 
vehicles, but iron-tired horse-drawn vehicles break them 
up badly. Repairs can be made where defects occur, 
and it is probable that the state of Massachusetts, whose 
records can be consulted on this subject, has had the 
most extended and successful experience in so doing. 



CHAPTER XI 
MAINTENANCE AND REPAIRS 

Asphalt surfaces, like all other street and highway 
surfaces require maintenance, and the extent of this 
maintenance will depend upon the character of the 
original construction, the wear and tear to which the 
surface is exposed, and the good judgment and skill with 
which it is carried out. The causes of deterioration are 
many and are discussed at length in ^^The Modern 
Asphalt Pavement/' 

Maintenance is required because of deterioration and 
repairs for the renewal of the surface where openings 
have been made for underground work. In a pocket- 
book it will only be necessary to make some suggestions 
as to how maintenance can be best carried out. 

In repairing cuts or surfaces which have been displaced 
in the course of public improvements, it is of great 
importance that trenches or openings disturbing the soil 
should be back-filled in such a way as to give an adequate 
support to the foundation. Of course the manner in 
which this can be most satisfactorily done will depend 
upon the nature of the soil. Sandy soils can be well 
compacted with the use of water, but this will not serve 
where the soil is of a clayey nature. The fills should 
be in courses of but a few inches in thickness and well 
rammed. Where the soil is of such a nature as to 
prevent an immediate compaction by ramming, a natural 

107 



108 ASPHALT CONSTRUCTION 

settlement should be awaited before placing the surface. 
In winter months this will, of course, always be necessary. 

The foundation placed upon the fill must be of the type 
of the original pavement, and carefully placed at a proper 
grade. It is sometimes rather ludicrous to observe the 
condition of an old foundation, either of concrete or 
stone blocks, when the surface is removed for renewal 
and where there have been many cuts during the life of the 
pavement. It will often look like a checker-board with 
elevations and depressions at different levels. That 
fills can be satisfactorily done is evidenced from replace- 
ment over trenches which have been excavated for laying 
large water mains, 48 in. in diameter, in old broken-stone 
surfaces, as on Broadway above 59th St. in New York 
City, but too often it is not so done and depressions in 
the new surface result in course of time under travel. 

In the case of maintaining sheet asphalt surfaces 
where there is no defect in the foundation, it is 
usually done in one or two ways, either by cutting out 
the defect, removing the surface mixture and binder and 
replacing the entire intermediate and surface coat, or 
the latter alone is softened by a heater and scraped off 
with a saw-toothed hoe for a depth sufficient to allow 
the application of at least an inch of new material. 

In the cutting-out process care should be taken to 
carry the cut back to good material which shall form a 
stable joint and give lateral support to the patch. The 
cutting instrument should be of such description that it 
will cut and not shatter the adjoining surface which is to 
remain in place. The cut should be perpendicular and 
not slope in toward the hole to be repaired as this will 
not furnish a satisfactory support. A feather edge of 
new material will not prove lasting. Cuts should be of 



MAINTENANCE AND REPAIRS 109 

rectangular shape and not rounded, not only on account 
of the unsightliness of the latter but because the rectan- 
gular cut is more stable. The edges of the cut should be 
carefully painted with asphalt cement and not merely 
daubed with it here and there, as is the usual practice, 
owing to the use of brushes or brooms which are quite 
unsuited for the purpose. The coating should be as 
thin as possible, and a softer cement than that in use for 
making the surface mixture will aid in accomplishing the 
painting properly. The necessity for perfectly painting 
the joints is often evidenced by the fact that repairs 
show their outline when improperly done as the surface 
begins to dry out after wet weather. 

The surface mixture which is used for the patch should 
have a mineral aggregate of the same grading as that of 
the original pavement, or approach it as nearly as possi- 
ble. The asphalt cement of which it is composed should 
correspond in consistency to that in the old surface, 
which will depend upon the age of the latter, being 
harder for an old surface than for a comparatively new 
one. Too soft a mixture will readily displace when used 
to repair an old and hard surface. Good judgment is 
most necessary in determining the amount of surface 
mixture to be placed in any cut. It should not be so 
large an amount that it will project above the old surface 
when it has been compressed under the roller, nor so 
small that the roller will ride on the old pavement and 
thus prevent proper compression of the new material. 
In the latter case the patch will at first absorb water in 
wet weather and later, being compressed by the travel 
under which it is subjected, will be depressed below the 
surface of the street which has been repaired. 

The difl&culty in making repairs over large areas where 



110 ASPHALT CONSTRUCTION 

the pavements are of different ages, is the fact that the 
surface mixture which may be suitable for one street of 
considerable age and consequent hardness, may not be 
satisfactory for another surface which consists of a softer 
mixture. 

In making repairs over small areas it will be found 
well to furnish the material from the plant in what arej 
known as ^^combination loads." The forward partj 
of the truck may be loaded with binder and the latter' 
with surface mixture, the two being separated by an 
old canvas or even, very satisfactorily, with heavy 
Manila paper. 

There are several types of surface heaters which are in 
use for softening the old surface. The preference for 
one or another merely depends upon the speed with 
which the work can be done and the area of old mate- 
rial which can be removed in a given time. In the 
writer's opinion, there is no superiority in the use of 
hot air over the direct flame method, as the lower 
layers of the surface are not injured by the flame if 
the burned and softened material is completely re- 
moved before applying the new surface. Work which 
has been under the author's observation and which 
was done fifteen years ago with a direct flame, is in 
satisfactory condition at the present time. Of course 
good judgment must be used in doing work of this 
description and the new surface work must be com- 
pleted before the bottom course upon which it is placed 
has become entirely cold. It is not, in the opinion of 
the writer, a desirable thing to apply a paint coat to 
the burned surface unless the cuts which have been 
burned out have become quite cold, as for instance, 
by not being filled until the day following that on which 



MAINTENANCE AND REPAIRS 111 

they have been made. Such an application of paint 
will frequently act as a lubricator and cause displacement. 

Repair work should not, of course, be done in wet or 
cold weather. Frequently much criticism is heard of 
the fact that the repairs are not immediately made to 
old sheet asphalt surfaces which have deteriorated 
rapidly during cold or wet weather in winter, but it 
would be injudicious in the light of the author's experi- 
ence, to attempt to do such repairs under unfavorable 
conditions. There are often winters which are dry and 
cold during which repairs can be undertaken at all 
times, and others in which it is impossible to do good 
work and inadvisable to attempt it. Under any cir- 
cumstances repair work requires great skilly long-time 
experience on the part of foremen and laborers in execut- 
ing it and good judgment as to what to replace and 
when to do it. 

Maintenance and repairs to broken-stone roads 
require as much care and good judgment as those to 
sheet asphalt surfaces. In the writer's opinion, spots 
that have disintegrated or become depressed, should be 
cut out in quite the same way as in a sheet asphalt 
surface, in order to obtain the proper lateral support 
for the patch. The cut should be filled with the same 
character of material as that which was used in the 
original construction of the surface, and not with coarser 
or finer material; as is sometimes done. 

As yet the application of surface heaters to the repair- 
ing of bituminous broken-stone or concrete roads has 
received very little attention. There seems to be no 
reason why heaters should not be used if the highest type 
of work is desired. 



CHAPTER XII 
THE PLANT 

To produce a satisfactory material from the compo- 
nents which are available for use as a road surface, some 
type of plant which shall meet certain imposed condi- 
tions is necessary. Provision must be made for heating 
the sand and stone with great regularity and uniformity 
without segregation, to such a temperature as will enable 
it to be satisfactorily mixed with an asphalt cementing 
material, to melt asphalt, heat flux and produce asphaltic 
cement, and maintain the latter in a melted condition at a 
uniform temperature with suitable means of agitation, 
to afford suitable means of determining the weight and 
volume of the constituents which are to compose the dif- 
ferent batches of the material and to provide a mixer 
which shall combine the components uniformly and 
homogeneously. 

It would hardly be justifiable to go into a description of 
the various types of plants which are available for this 
purpose at the present time. Many of them comply 
with the requisites which have been laid down. The 
important point to be considered is: they should be of 
such capacity as to furnish adequate suppKes of all the 
components which are to be used, and in such quantities 
and in such condition that no delay shall ensue in meeting 
the demands of the mixer. The sand should be heated 
in a uniform manner and after collection in a storage bin 
should have the proper temperature, neither too hot nor 

112 



THE PLANT 113 

too cold, the extreme in cold weather being not over 380° 
F. and in warm weather not below 325° F. The success 
with which sand is heated will depend largely on the 
skill of the fireman who manipulates the fires, and the 
output should be carefully watched as to temperatures 
by means of thermometers. The plant should possess 
sufficient storage capacity for hot sand in the way of bins, 
so that it can be accumulated in considerable amounts be- 
fore proceeding to turn out surface mixtures, as this will 
not be done satisfactorily if delays are incurred while wait- 
ing for a supply. Care should be taken to see that in pass- 
ing through the sand drums and in storing it in the bins, 
segregation does not take place ; that is to say, that the 
coarser particles do not collect at one point and the finer 
ones at another, thus preventing uniformity in the sand 
grading as it is supplied to the mixer. 

In case asphaltic concrete is turned out provision 
must be made for separating the heated stone into at 
least two sizes. This can be accomplished by passing 
the stone as it comes from the drums over revolving 
screens having a pitch of 3/4 in. to i ft., and 6 ft. long, 
3 ft. of which is covered with metal perforated with 
i/8-in. openings to separate sand, and the other 3 ft. 
with 3/8-in. perforations to separate stone of small size, 
the tailings consisting of the larger stone. The three 
sizes of aggregate are then combined in the required 
proportion by weight or measurement. 

It is usually advisable, however, not to heat the 
stone and sand in the same drum, as under such circum- 
stances the stone becomes much too hot by the time 
that the sand is heated to a sufficient temperature. It 
is preferable to heat the stone and the sand separately. 

The tanks for maintaining the asphalt cement in 



114 ASPHALT CONSTRUCTION 

melted condition should be so constructed that no por- 
tion of their contents will become overheated at any 
point, although this should ordinarily be avoided by suit- 
able agitation, as has been mentioned in the chapter on 
asphalt cement. With smaller portable tanks, where 
asphalt is melted alongside the road as in bituminous 
highway construction, and where no power agitation is 
possible, agitation by hand should always be provided. 

In permanent plants of the highest grade the asphalt 
is melted and fluxed in tanks which are provided with 
coils of pipe carrying steam under high pressure, 125 lb. 
to the square inch, and the agitation is dry steam. This 
permits of fluxing asphalt at a moderate temperature and 
of maintaining it in the same way for a considerable 
period of time without danger of its becoming harder in 
consistency. The tanks from which the asphalt is dipped 
and measured for use in making surface mixtures are 
filled from those which are heated by steam. The dip- 
ping tanks should be fired carefully and should be cleaned 
at intervals from any sediment forming upon the bottom, 
not only for the reason that it preserves the tank itself 
but also admits of lighter firing to maintain the asphalt 
cement at the proper temperature and consequent re- 
duction of the danger of overheating the material. 

The character of the mixer in use in combining the hot 
components is of great importance, and equally so the 
fact that it must be maintained in the best condition. 
It should have a liner which can be replaced when worn 
and the teeth should always be raaintained of such length 
that they are not separated from the finer by more than 
a quarter of an inch in the case of the surface material, 
although a wider space must be provided where a mixture 
containing or consisting of stone is provided. This can 



THE PLANT 115 

be regulated by the introduction or removal of shims 
under the bearings of the shaft upon which the teeth are 
fixed, as may be necessary. 

The best practice provides for the use of one mixer for 
producing surface material and another for stone mix- 
tures, such as open and close binder or asphaltic concrete. 
Where this is not the case an interchangeable shaft 
must be provided which has teeth of a proper length 
for the stone mixture to replace those in use with the 
sheet asphalt mixture. 

Provision must be made for the proper storage in a 
perfectly dry condition of the supply of filler, and pro- 
vision made for measuring it, usually by volume. 

All the components in the mixture should, preferably, 
be weighed, but it is usual to confine this to the asphalt 
cement, the sand being measured by volume, the weight 
of which is known, and the filler in a similar way. 

The proper volume or weight of sand, the temperature 
of which has been shown to be satisfactory by a ther- 
mometer, is introduced into the mixer, and immediately 
followed by the proper amount of filler. The sand and 
the filler are allowed to mix for at least fifteen seconds. 
After the mixture of the two is homogeneous and the 
filler has attained the temperature, or approximately 
so, of the sand, the weighed amount of asphalt cement 
is added, and the three components mixed for thirty 
seconds, or longer, and until the material is homogeneous. 

The character of the material which is turned out 
will depend as much on the skill of the foreman who is 
managing the plant as upon the plant itself. The writer 
has seen better mixtures produced by a skillful foreman 
with a very poor plant than by a careless one in the 
best type of plant. Constant vigilance is necessary 



116 ASPHALT CONSTRUCTION 

to control the character and temperature of the com- 
ponents which are going into the mixture. To insure 
the most satisfactory results the plant should be pro- 
vided with facilities for so doing, for the use of the yard 
foreman, adjoining the platform on which the mixing 
is done, or nearby. Thermometers for taking tempera- 
tures must be available. A set of sand screens should 
be at hand for controlling the sand grading; a proper 
outfit, either a penetration machine or a float plate, 
for controlling the consistency of the asphalt cement, 
and Manila paper suitable for making pat tests of the 
mixture, in a manner previously described, so that he 
can control the amount of asphalt cement in use. Very 
frequent tests of grading of the sand, its temperature, 
the consistency of the asphalt cement and the amount 
in the mixture, should be conducted. Such tests cannot 
be neglected if the output is expected to be satisfactory 
and uniform, and this is recognized as seen from the 
directions of a concern given in the '^Instructions for 
Plant Foremen and Chemists" which have been pre- 
viously quoted. 

In the production of the binder, whether of the open 
or close type, the same care must be exercised. In pro- 
ducing open binder the stone should not be too hot so 
that the asphalt cement will run ojBf it on hauling to the , 
street. The production of asphaltic concrete, whether 
for use as a close binder or for a surface course, requires 
greater care, involving all the considerations entering | 
into the preparation of the ordinary type of sand mix- j 
ture, but sufficient has been said in regard to this in ' 
another chapter to show its importance. ! 



CHAPTER XIII 

WORK UPON THE STREET 

The material produced at the plant, whether binder or 
surface mixture, must be transported to the street in such 
a way as to preserve as nearly the same temperature 

i that it had on leaving the plant. To accomplish this 
canvas covers should be provided for the trucks in which 
the material is hauled. That it has the proper tem- 

j perature must be determined with a thermometer on 
its arrival at the street, and the street foreman should be 
convinced that the temperature is satisfactory before he 
puts it in place. Usually the larger the amount of 
material contained in a load the better. the temperature 
will be preserved but, on the other hand, the larger the 
load the more it becomes compacted during its haul to the 
street, and the more difficult it is to break it up and rake 
it out. The disadvantage, in this direction, of large loads 
must be considered, especially if the hauls are long. A 
I sheet asphalt surface mixture or an asphaltic concrete 
will, of course, suffer more in this way than an open 
I binder. Under any circumstances the most important 
consideration in laying a street surface is to see that the 
mixture or close binder is completely loosened up and 
spread evenly with rakes before the use of the roller is 
'permitted. The waviness which is so common in many 
[I bituminous surfaces is due to the fact that the hot mate- 
rial is not completely raked out. Mixtures should be 
dumped so far from the point where they are to be placed 

117 



Vi 



118 ASPHALT CONSTRUCTION 

eventually, that they must be entirely shoveled over. 
Rakes with long teeth should be used, and every portion 
of it loosened up so that no lumps of compacted material 
remain. The workmen should not be allowed to walk 
or place their feet in the hot mixture for the purpose of 
reaching out to correct some defect. Such depressions 
will be filled by the raker, leaving more material at these 
points than elsewhere. Under travel the more slightly 
compressed material will be depressed, and unevenness 
in the surface of the work will eventually become ap- 
parent. In the extended experience of the writer, a 
satisfactory result will only be obtained by constant 
attention on the part of the street foreman to these 
conditions. The care expended on supervision and regu- 
lation of the distribution of the hot material will give a 
return which cannot be accomplished in any other way. 

The temperature of a surface mixture on the street 
should be not less than 300° F. for one prepared with 
Bermudez asphalt. A Trinidad mixture may be laid at a 
temperature of from 325° to 340° F. more satisfactorily, 
at least if it has a dense mineral aggregate, although 
some of the poorer mixtures in each case may undoubt- 
edly be laid at much lower temperatures. 

If a sheet asphalt surface contains a sufficient amount 
of filler and if the sand is of a satisfactory grading, the 
original compression of the material may be carried out 
at once with a steam roller, as such a mixture will not , 
displace under it, but with some of the coarser mixtures 
a Kghter roller may first be necessary. 

The rolling and compression of a sheet asphalt surface 
require great experience and skill on the part of the roller 
engineer in order to produce a satisfactory surface but 
such a person cannot obtain satisfactory results if the ||j 



WORK UPON THE STREET 119 

materials have not originally been distributed by the 
rakers with great care. It is impossible here to give in 
any adequate manner a description of how rolhng should 
be done. It is something that must be acquired by 
experience. It is needless to say that the roller should be 
so manipulated as to produce no waves in the pavement, 
which will often happen if the roller is stopped or started 
suddenly. Where the width of the street permits, cross 
rolHng as well as longitudinal should be practised. It is 
questionable if it is desirable to roll a sheet asphalt sur- 
face too much after it has cooled to a certain point. 
Travel will accompHsh the necessary compression after 
the street has been opened, and without danger of pro- 
ducing some of the defects which may be attributed to the 
steam roller. It must be remembered that the weight 
upon the iron tires of a truck is greater per inch tread than 
that of the steam roller, which is so widely distributed 
per inch run. Travel and traffic will, therefore, accom- 
pHsh much which the roller cannot. As has been said, 
travel over a sheet asphalt surface will bring out many of 
the defects which are not visible after the steam roller has 
finished its work. 

Provision is frequently made that cement or lime- 
stone dust be scattered over the surface before it is 
rolled, and that the gutters be painted for a certain 
width with asphaltic cement. In the experience of 
the writer in England and on the Continent, both of these 
provisions involve expense with no adequate return. 
The surface can be rolled as satisfactorily without 
dusting, and perhaps more so. The desired color of 
the surface will be produced by a few^days travel of 
vehicles and by the natural dust which accumulates 
there. A paint coat on the gutters, where the mixture 



120 ASPHALT CONSTRUCTION 

is satisfactory, is quite unnecessary and involves a 
useless additional expense. Modern asphalt mixtures 
are not susceptible to water action if proper provision 
is made for grades so that water will not stand in pools 
for any length of time, and this, of course, is something 
that the municipal engineer should provide for. The 
gutters on lower Fifth Avenue, New York, have been 
exposed to travel and the elements for fifteen years, 
and show no signs of deterioration. 

Finally, a warning must be given against the use of 
hot smoothing irons upon a sheet asphalt surface. The 
closing up of any slight porosity will take place under 
traffic, whereas the smoothing irons, while closing up 
such places do very serious damage to the surface 
with which they come in contact. Their use should be 
abandoned as it is merely an excuse to cover up poor 
work. This should be prevented in sjme other way. 



CHAPTER XIV 

ADVICE TO ENGINEERS, CONTRACTORS AND 
INSPECTORS 

Suggestions to Engineers. — Based upon an extended 
experience in the construction of asphalt surfaces, the 
writer would suggest to engineers that in preparing 
specifications they be made as simple and as free from 
verbiage as possible, to avoid diflSculties in their interpre- 
tation. Frequently they carry expressions which have 
been handed down from year to year through a series 
of specifications and which, in the light of modern 
practice, have little or no meaning. Clauses which 
can be interpreted in different manners should be 
eliminated. Materials should be specified specifically. 
For example, a specification should not call for Portland 
cement or ground limestone as a filler, the alternative 
materials being of very different value and cost. In 
any contract only one should be provided for. It would 
be as absurd to permit the use of a natural or Portland 
cement concrete foundation as the permissible use of 
one or another filler. The same may be said in regard 
to permitting bids on different asphalts of different 
origin and value. The engineer should know which 
type of material he desires, whether one corresponding 
to Portland cement or that corresponding to a natural 
cement. Unfortunately local legislation does not usu- 
ally permit of this and the result is that that locality 

121 



122 ASPHALT CONSTRUCTION 

where the contract must be awarded to the lowest 
bidder gets the cheapest type of construction instead 
of the best. As long as such laws remain on the statute 
books the highest type of construction will not be attained. 
The locality will obtain a pavement which corresponds 
to a $3 pair of shoes instead of one corresponding to 
a $5 pair. 

The engineer should base his specification on service 
tests and experience in the construction of asphaltic 
surfaces. If not of extended experience himself he should 
be guided by that of others, accommodating their results 
to the local conditions which he must meet. Standard 
specifications of various societies may be used as a guide, 
but not blindly. As has been said in another chapter, the 
type of surface constructed should be designed for the 
condition which it is required to meet. Under the most 
trying conditions an expensive pavement may, eventually, 
be more economical than a cheaper form, whereas under i 
others the reverse may be the case. Good judgment is, 
therefore, essential in deciding upon what is to be called 
for. 

The engineer, unfortunately, is not always given the 
widest liberty in laying down the policy to be followed, 
but must accommodate himself to the ideas of officials 
over him who have little knowledge of pavement con- 
struction. It must be remembered that the economic 
value of any pavement will not be demonstrated until 
the pavement is worn out. It is only then that a de- 
termination is arrived at as to how many tons of travel 
the surface has carried during the period of its existence, 
and what this has cost. The paving problem is one ex- 
tending over a long period of years, and that locality will 
be best served which gives its engineer such tenure of 



ADVICE 123 

office that he can follow it through a long period of time. 
The short tenure of office of many of our municipal and 
state highway engineers is responsible for changes of 
policy at intervals which are destructive of economy. 

Tests for materials should be so prescribed that only 
the material which the engineer desires will comply with 
them. It would be foolish to write a specification for 
cement which would admit both Portland cement and 
natural cement. It seems equally so to write a specifica- 
tion for asphalt which will admit with the highest grade 
material some of the lower priced industrial residuals. 
The engineer should decide what he wishes and specify 
either one or the other, in the case of asphalt as well as 
in the case of hydraulic cement. Unfortunately, public 
opinion, and the law^ in many cases, do not recognize this 
fact and the result is great confusion in many specfiica- 
tions which are drawn, and in the subsequent awarding 
of a contract of which they form a part. Education of 
the public in this respect is most necessary, and it is 
the engineer who can undertake it most satisfactorily. 
Before specifications are issued, all persons, contractors, 
citizens and others, should have an opportunity to see 
and discuss them and make objections to them, to insure 
their reasonableness. 

Suggestions to Contractors. — ^A contractor who engages 
in the construction of sheet asphalt pavements and as- 
phaltic concrete or broken-stone highways, should put 
himself in close relation with the engineer who draws the 
specifications and should, where it is possible, enter any 
objections to thembefore they havebeen advertised. The 
combined judgment of the two should result in a specifi- 
cation which can be carried out satisfactorily in a prac- 
tical way without arousing contention. The engineer 



124 ASPHALT CONSTRUCTION 



1 

him « 



can name what he wishes, and the contractor can tell him 
what it is possible for him to do with satisfaction. 

The contractor, if he wishes to remain in the business 
for an indefinite period, and to establish a reputation for 
doing the best work, will take pride in seeing that the 
specifications are closely complied with, and that the 
asphaltic surface which he constructs will be a credit to 
him, not only for the period during which it is under 
guarantee, but for years afterward. He should see that a 
surface laid under a five-year guarantee will not only go 
through this period with a low cost of maintenance, but 
shall continue to do so for many years afterward. On 
the other hand, the contractor is frequently hampered by 
rulings of the engineer or his inspectors, through the 
latter's ignorance. Cases have come to the attention of 
the writer where attempts or willingness of the contractor 
to do better work than the specification called for, have 
not been appreciated, and such work has even been ruled 
upon as not complying with the specifications on this 
account. The contractor must, therefore, in many 
instances, confine himself absolutely to the terms of the 
contract where, by increasing somewhat the cost to him- 
self he might do a much better job, and one which would 
be more to his credit. In every case, of course, the con- 
tractor must so conduct his operations as to avoid any 
possibility of litigation and the hair-splitting which is too 
often the object of an engineer or inspector who desires to 
demonstrate his own importance. 

Suggestions to Inspectors. — It is the duty of the 
inspector to observe, for the benefit of the engineer, the 
character of the materials which enter into any piece 
of asphaltic construction over which he may be placed, 
and the workmanship and manner in which they are 



ADVICE 125 

put in place but he should be a tactful man and aid 
rather than hinder the contractor in his work, report- 
ing to the engineer any defects in materials or work- 
manship which he has observed, but rarely attempting 
to give direct orders to the contractor or his em- 
ployees. His deaHngs with the latter should be 
more in the nature of suggestions than orders. The 
orders should come directly from the engineer or from 
his immediate assistant. Inspectors when they use 
their authority along these lines may be of the greatest 
assistance to both contracting parties, but otherwise 
a great hindrance. The inspector should be thoroughly 
informed in regard to the character of the materials 
in use in any piece of work which he is supervising, and 
in regard to the form of construction employed. It is 
for the purpose of instructing him in this direction 
that the present work is prepared. 

Suggestions to Citizens. — It may be suggested to 
the citizen that the economics of pavement and highway 
construction is a subject which should be carefully 
considered before that of the actual cost at which any 
piece of work is done. The citizen, as a rule, does not 
appreciate that a sheet asphalt surface, for instance, 
which may cost under a certain specification 50 cents 
a square yard more than another under a different 
specification, is really more economical than the cheaper 
form. The illustration which has been used before, 
comparing the two surfaces to shoes which cost $3 and 
$5 per pair, may again be used. The more expensive 
materials in the dearer shoes will give more lasting 
and more economic results than those obtained with the 
inferior material. Of course, there are conditions 
under which the cheaper material may be employed 



126 ASPHALT CONSTRUCTION 

economically, comparable for instance to a situation 
where the shoes would be subjected to only slight wear 
and tear, or where the locality is so situated financially 
as not to permit of the purchase of a high-grade material. 
If a city's streets were in the hands of a business manager 
with a permanent tenure of office, and he was responsible 
for the financial result after a period of twenty years, 
it would seldom be the case that the least expensive form 
of pavement would be constructed. There is nothing 
which contributes so much to the unsatisfactory results 
obtained in many localities as the necessity for accepting 
the lowest bid for construction work. The selection 
of the type of pavement and the contractor who will 
do the work should be left to the judgment of the engi- 
neer, if he is a man of ability and good judgment, and 
is to retain his tenure of office for a long period of time. 
Unfortunately these conditions rarely exist and the public 
are the victims of the present situation, which is not 
one which would be tolerated by a private corporation. 



CHAPTER XV 

LABORATORY 

At a plant which is to pro\dde material for any large 
area of work a laboratory should be provided for pur- 
poses of control, and some one, chemist or inspector, 
should be available who should be experienced in the use 
of the apparatus. Such a laboratory can be installed at 
very moderate expense, and involves the purchase of the 
following apparatus: 

I Chaslyn balance, Eimer & Amend No. 21 71. 

1 Baker's scale, Eimer & Amend No. 2148. 

2 Bunsen burners, E. & A. No. 2597 (see note). 

1 set sieves — 200, 100, 80, 50, 40, 36, 20, 10, 4 and 2 

mesh, (Howard & Morse, Brooklyn, N. Y.). 

2 thermometers for penetrometer, 212° F., E. & A. 

No. 4894. 
I doz. 2 1/2-in. glass funnels, E. & A. No. 3345. 
I doz. watch glasses to cover funnels, E. & A. 

No. 7189. 
I doz. Erlenmeyer flasks, Jena glass, 200 c.c, E. & A. 

No. 3863. 
I N. Y. Testing Laboratory miniature penetrometer, 

Howard & Morse, Brooklyn. 
1/2 doz. 4 1/2-in porcelain evaporating dishes, E. & A. 

No. 2963. 
1/2 doz. watch glasses to cover dishes, E. & A. No. 

7189. 

127 



128 ASPHALT CONSTRUCTION 

1/2 doz. Royal Berlin porcelain crucibles No. o, 

without covers, E & A. 2850. 
4 Royal Berlin crucibles No. 2, without covers, 

E. & A. No. 2850. 
4 packages filter paper, S. & S., No. 597, E. & A. 

No. 3213 (9 cm.). 
1/2 doz. porcelain Gooch crucibles ( 40 c.c.) E. & A. 

No. 2852. 

1 pair tongs, E. & A. 2883-B. 

2 iron ring stands, E. & A. No. 4812. 

2 iron sand baths, 6 in. deep form, E. & A. No. 4555. 
I spatula, 4 in. E. & A. No. 4643. 

I spatula, 6 in. E. & A. No. 4643. 
I spatula, 8 in. E. & A. No. 4643. 
1/2 lb. asbestos for Gooch filters. 

3 clay triangles, small, to fit R. B. crucible No. o, 

E. & A. No. 4965. 

3 clay triangles, large, to support porcelain evapo- 
rating dishes, E. & A. No. 4965. 

I N. Y. Testing Laboratory dr3^ng oven, E. & A. 
No. 2073-d (see note). 

I gross 3 oz. deep seamless tin boxes, E. & A. No. 
2482. 

1 gross 2 oz. seamless tin boxes — E. & A. No. 2482.' 

2 chemical thermometers — 600° F., E. & A. No. 

4882. 
1/2 doz. camel's hair brushes, large size, E. & A. No.! 

2493. 
I Cleveland cup oil tester, E. & A. No. 4162, gas 

or alcohol lamp. 
1/4 lb. glass tubing, 3/16-in. diameter. 
1/4 lb. glass rod, i/8-in. diameter. 

I washing bottle, i quart, E. & A. No. 7 181. i 

li 

i 
.._.._... . . I 



LABORATORY 129 

50 lbs. carbon disulphide. 

10 ft. rubber tubing, 5/16 in., E. & A. No. 4540. 

I drum for carbon disulphide. 

I N. Y. Testing Laboratory extractor for asphaltic 

concrete, Howard & Morse. 

Note, — If a gas supply is not available, substitute two 

Barthel's alcohol burners, E. & A. No. 2544, small, for 

the Bunsen burner and tubing; also omit drying oven 

No. 2073-d. 

The methods which should be employed in utilizing 
this apparatus are ordinarily few in number and do not 
demand extreme skill but rather a certain amount of 
experience on the part of the operator. They are de- 
scribed in numerous publications, and will be found in 
the writer's work ^^The Modern Asphalt Pavement." 
Those which are in use in ordinary control work are 
given in the next chapter. 

With such a laboratory available there should be pos- 
sible a control of the consistency and uniformity of the 
asphalt cement, of the percentage of bitumen and grading 
of the mineral aggregate of the surfaces mixtures which 
are turned out, as well as the supplies of sand and of the 
raw materials which are received at the plant. Without 
such a laboratory the highest type of work cannot be 
accomplished. 



CHAPTER XVI 

METHODS FOR EXAMINATION OF BITUMINOUS 
MATERIALS AND MINERAL AGGREGATES 

Mesh Composition of Mineral Aggregate. — The 

determination of the grading of sand or of the fineness 
of a filler, is done with a series of sieves, which have 
been described on page 26. The operation of sifting 
and weighing the sand is conducted as follows: 

From 50 grm. to 500 grm. of the sand or crushed stone 
is weighed out on a satisfactory balance sensible to half 
a gram. It is thrown upon the 200-mesh sieve, the open- 
ings of which have been previously freed from very fine 
particles with a stiff brush. It is shaken from side to 
side, held in one hand and striking it between each 
movement against the palm of the other hand, and 
hitting it sharply on the table or on a hard surface from 
time to time to dislodge any particles which have filled 
the meshes but will not pass through. The sifting is 
done over a clean piece of paper to determine when 
further particles fail to pass the sieve. Any lumps of 
material which readily break up under the fingers should 
be so treated. When nothing further passes the sieve 
it will be found that some material will remain in the 
meshes of the wire cloth. This is allowed to remain 
there as being more nearly the size of the grains passed 
by this sieve than the next larger. It is rejected when 
the cloth is brushed for the next use of the sieve. The 
percentage of material passing the 200-mesh screen is 

130 



METHODS FOR EXAMINATION 131 

arrived at by weighing the portion which will not pass 
and deducting this from the original weight, 50 grm., 
from which the percentage of this material may be 
readily calculated. 

The 200-mesh screen is used first for the reason that 
the fine material must necessarily be removed first from 
the coarser particles to which it may adhere, and because 
some of it may be lost by blowing away in the process 
of sifting. It is determined by the loss of weight rather 
than by direct weighing, for the same reason. In sifting 
fine material to be used as a filler, some coarse material 
should be placed in the sieve, such as a few pennies or 
some shot, to aid in breaking up the lumps and assist 
in screening. 

After the use of the 200-mesh sieve the others are 
employed in order of size, and the percentage passing 
each of the screens determined by the loss in weight 
which occurs. 

The grading of the mineral aggregate of sheet asphalt 
mixtures is determined in the same way as that of sand, 
after the removal of the bitumen by solvents. 

Where the aggregate carries coarser material than 
sand, this is usually removed by separating it with a 
lo-mesh sieve before screening the finer portion, as the 
coarser particles would injure the cloth of the finer sieves. 

The entire operation can be carried out by mechanical 
contrivances, and this is frequently advisable with the 
coarser aggregates but is not so satisfactory, in the 
author's opinion, with those which are finer and which 
are found in a sheet asphalt mixture. 
I Material Finer than that Passing 200 Mesh in a 
I Filler. — The actual fineness of the dust of the filler can- 
not be determined solely by the use of a 200-mesh 

f 



132 ASPHALT CONSTRUCTION 

screen, as such a screen allows the passage of particles 
of sand which are not fine enough to be considered a 
filler. The finer material can, however, be determined 
by elutriation with water. Five grams of the filler 
are placed in a beaker holding about 600 c.c. and about 
120 mm. high. The beaker is nearly filled with distilled 
water of a temperature of 68° F. and agitated with an 
air blast until the filler is suspended, avoiding a rotary 
motion of the water. On stopping the blast the liquid 
is allowed to settle for fifteen seconds, when the water 
is poured off as quickly as possible without carrying 
any of the sediment. The washing is repeated twice. 
The residue is then washed out into a dish, dried and 
weighed. The loss represents the impalpably fine 
material which will serve as filler. 

Total Bitumen in Refined Asphalt and Asphalt Cement. 
— One gram of the dried or refined material, in a state 
of fine powder, if possible, is weighed out and intro- 
duced into a 200 c.c. Erlenmeyer flask of Jena glass and 
covered with about 100 c.c. of carbon disulphide. It 
is then set aside for at least five hours, or overnight, 
at the temperature of the laboratory. In the meantime 
a Gooch crucible is prepared with an asbestos felt and 
weighed. The felt is made by beating up long-fiber 
Italian asbestos in a mortar, and suspending the finer 
particles in water and quickly pouring off from the 
coarse particles. Too much of the latter should not 
be removed, or the felt will be too dense. The decanted i 
asbestos and water can be kept in a bottle for use. To i 
prepare the felt the asbestos and water are shaken up i 
and what is found to be a proper amount poured into ' 
the crucible, which has in the meantime been attached ' 
to a vacuum filtering-flask by the proper glass and rubber |j 



METHODS FOR EXAMINATION 133 

connections. As soon as the asbestos has somewhat 
settled the vacuum-pump is started and the felt firmly 
drawn on the bottom of the crucible. It is then dried, 
ignited, and weighed. 

After standing a proper time the disulphide is decanted 
very carefully upon the filter which is supported in the 
neck of a wide-mouth flask and allowed to run through 
without pressure. The flask after being tipped to pour 
the first portion is not again placed erect in order to 
avoid stirring up the insoluble material, but is held 
at an angle on any suitable base, such as a clay chimney. 
After all the disulphide has been decanted more is added 
and the insoluble matter shaken up with it. This is 
allowed to settle and decanted as before, the insoluble 
matter being finally brought on the filter and washed 
with the solvent until clean. The excess of disulphide 
is allowed to evaporate from the Gooch crucible at the 
temperature of the room. It is then dried for a short 
time at ioo° C. and weighed. The loss of weight is the 
percentage of bitumen soluble in CS2. 

In the meantime, however, the disulphide which has 

passed the filter is allowed to subside for twenty-four 

hours, if possible, and is then decanted carefully from 

the flask in which it has been received into a weighed 

platinum or unweighed porcelain dish. If there is any 

sediment in this flask it must be rinsed back into the 

Gooch crucible with disulphide and the crucible again 

washed clean. The solvent in the dish is placed in a 

1 good draught and lighted. When all the disulphide 

has burned, the bitumen remaim'ng in the dish is burned 

I off over a lamp and the mineral residue, which was too 

( fine to subside, is weighed, if the burning was done in a 

platinum dish, or dusted out and added to the crucible 



r 



134 ASPHALT CONSTRUCTION 



if in a porcelain one. In the former case the weight is 
added to that of the Gooch crucible or subtracted from 
the per cent, of bitumen, found without its consideration, 
as a correction. Care must be used in this method of 
procedure that the solvent does not creep over the sides 
of the crucible and that the outside is free from bitumen 
before weighing. f 

Mineral Matter or Ash. — One gram of the same 
sample of material used for the determination of bitumen 
is weighed out in a No. o Royal Berlin porcelain crucible 
and burned in a mufHe or over a flame until free from 
carbon. This must be determined by breaking up the 
cake of ash, moistening with water or alcohol, and 
observing if any black particles of coke are present. 
The weight of the residue is stated as inorganic or mineral 
matter. 

The determination is of course not exact, sulphuric 
acid and the alkalies being volatilized in many cases, 
but it is satisfactory for technical purposes. 

Consistency or Penetration of Asphalt Cements. — The 
consistency of an asphalt cement is determined by the 
depth in hundredths of a centimeter to which a No. 2 
cambric needle will penetrate in five seconds, under a 
weight of 100 grm. at 77° F. The Dow penetration ma- 
chine or the New York Testing Laboratory penetrom- j 
eter may be used for this purpose, the results being the j 
same with either, the latter being, in the opinion of the 
writer, more satisfactory because of its greater stability 
and the greater ease with which the surface of an asphalt | 
cement is brought in contact with the needle. The 
asphalt cement is contained in an open box similar in 
shape to those in which shoe blacking is usually supplied, 
at least 2 1/4 in. in diameter and of sufficient depth to j 

i 



METHODS FOR EXAMINATION 135 

permit of the penetration of the needle without reaching 
the bottom. Before being placed under the needle the 
surface is perfected by melting and brought to the 
proper temperature by immersion in water at 77° F. for 
a sufl&cient length of time to acquire this temperature. 
It is placed upon the support of the penetrometer, the 
needle brought nearly in touch with it, and then elevated 
by the screw until contact is attained. The needle with 
its weight is then released by a movement of the clamp 
and the time limit marked by a metronome, or otherwise. 
Before releasing the needle the height at which it stands 
is read off upon the dial with which the instrument is 
provided, and the drop again measured after penetration, 
on the same scale. Some experience is necessary in using 
the apparatus satisfactorily, but it can be readily acquired. 

Flow Test. — The consistency of asphalt cement can be 
controlled, as has been said in a previous chapter, by 
means of comparing the length to which a cylinder of it 
will flow with that of a material of standard consistency. 
The cylinders are made in a split mould of turned brass. 
They are 3/4 in. long and 3/8 in. in diameter. They are 
placed on a brass plate with corrugations corresponding 
in size to that of the cylinder, being careful to see that 
they adhere thereto so that they will not slip when warmed. 
The corrugated plate is then exposed at an angle of 
45° to a temperature at which the cements will flow. The 
relative lengths which the standard and the asphalt 
cement to be tested reach, is an indication of how nearly 
the consistency of one corresponds with that of the other. 
If the cement is harder than the standard it will not flow 
so far; if it is softer it will, of course, flow further. 

Examination of Sheet Asphalt Surface Mixtures. — 
Specimens of sheet asphalt surface mixtures are examined 



136 ASPHALT CONSTRUCTION 

as regards the percentage of bitumen and the grading 
of the mineral aggregate as follows: 

The amount of bitumen is determined with the labora- 
tory equipment which has been suggested by placing lo 
grm. upon a Schleicher & Schiill 9 cm. 597 filter paper 
folded in a funnel 2 1/2 in. in diameter with a short 
stem, supported in a conical fiat bottom assay flask 
holding about 250 c.c. With a washing bottle provided 
with two tubes through its cork, one reaching to the bot- 
tom of the bottle and the other only just passing the cork, 
but with a capillary orifice, a small stream of disulphide of 
carbon can be delivered on inverting the flask without 
the necessity of using pressure from the mouth and in- 
haling the noxious vapor of the solvent. With this 
bottle a fine stream is directed on the surface mixture 
but no more than it can absorb. It is allowed to stand 
until it has softened and settled upon the filter. The 
latter is then filled up to an eighth of an inch below the rim 
and the funnel covered with a 2 1/2-in. watch-glass. It 
is not filled up at first, as before the mixture has been 
softened and settled upon the paper the solvent would 
have run through the filter paper and would not have been 
used economically. As the percolation goes on the sol- 
vent is renewed and if it goes too slowly the rate may be 
hastened by washing between the paper and the funnel 
with disulphide, which will dissolve the bitumen, which 
may have hardened and closed the pores by evaporation, 
or by lifting the filter a little and letting it drop back. 
On the day the analysis is started the sand is washed as 
clean as possible, but nothing more is done. The filter 
with the sand and the percolate is allowed to stand over 
night to permit anything that has run through to settle 
out. 



METHODS FOR EX A MINA TION 137 

In the morning the funnel is placed in a clean assay 
flask and the percolate is carefully [decanted into 
a correction bottle, being careful not to disturb the 
sediment. 

Some disulphide of carbon is poured on this, it is shaken 
up and poured back on the filter, the first assay flask 
being thoroughly cleaned with a feather and everything 
brought upon the original filter paper. The mineral 
aggregate is washed clean with the solvent. 

The percolate, or solution of bitumen, in disulphide 
of carbon is poured from the correction bottle into a 
dish, burned, ignited, and the correction obtained. 

In the meantime the mineral aggregate after drying 
is separated from the filter over a piece of glazed paper 
by scraping with a blunt spatula or rubbing between 
the fingers in an appropriate way until all the mineral 
matter that can be removed is separated, taking care, 
of course, not to detach any fibers of the paper. It is 
then dusted into a weighed No. 2 Royal Berlin porcelain 
crucible and set aside. The filter paper, containing 
much fine mineral matter in its pores, is burned either 
with the correction in its dish or in any satisfactory way, 
its ash and the correction added to the mineral aggregate 
and the crucible's entire contents, after one is assured 
that no trace of solvent remains, are weighed. The 
difference in the weight of the aggregate and the 10 
grm. of surface taken is that of the bitumen and gives 
the per cent, of bitumen in the mixture, which should 
be calculated to the nearest tenth of i per cent. 

The grading of the mineral aggregate is readily deter- 
mined with sieves in the same manner as that of sand. 

Examination of Asphalt Block Mixtures and Asphaltic 
Concrete. — In the case of mixtures carrying stone a 



138 



ASPHALT CONSTRUCTION 




METHODS FOR EXAMINATION 139 

different method of procedure is necessary than with 
the sheet asphalt surface mixture. The following one 
has been devised by Mr. C. N. Forrest of the New York 
Testing Laboratory. 

The quantity of stone mixtures^ which should be 
taken for analysis will depend upon the size of the 
largest particles of the mineral aggregate. The sample 
should be warmed until it is sufficiently soft to be 
readily broken apart by hand without fracturing the 
stone; 200 to 300 grm. of asphalt block or similar 
mixtures and 500 grm. of asphaltic concrete is an appro- 
priate quantity for the analysis. 

The New York Testing Laboratory extraction device, 
shown in the illustration on page 138 is a modification 
of the Wiley extractor. It is manufactured by Howard 
& Morse, Brooklyn, N. Y. The sample for analysis is 
packed in the wire basket and covered with a mat of 
absorbent cotton 1/4 in. thick. Place 100 c.c. carbon 
disulphide in the interior vessel B.B. and suspend the 
wire basket containing the sample from the hooks in 
the upper part of that portion of the device. The con- 
denser D.D. covers B.B, loosely and cold water should 
be circulated through it. A i6-candle-power incan- 
descent lamp in A, A, will vaporize the solvent which 
thereby rises to the condenser and falls back upon the 
sample extracting the bitumen therefrom. 

About three hours are required to effect complete 
extraction, after which the solvent is permitted to 
evaporate from the mineral aggregate spontaneously 
and finally, completely expelled by warming in an oven. 

The extract is burnt in a porcelain dish and the mineral 
matter thus recovered, which had passed through the 
wire basket. 



140 ASPHALT CONSTRUCTION 

The combined weight of this correction and the 
mineral aggregate in the basket, less the quantity 
taken will give the amount of bitumen present in the 
sample. 

The extracted mineral aggregate may then be screened 
as previously described. 

The methods which have been described are those which 
will be ordinarily used at the plant to control its output. 
Other necessary determinations must be made in a well- 
established laboratory, and descriptions thereof at length 
are given in the author's work ^^The Modern Asphalt 
Pavement" and elsewhere. 



CHAPTER XVII 

INSTRUCTIONS FOR TAKING SAMPLES AND 

SPECIMENS OF MATERIALS FOR 

EXAMINATION 

Samples and Specimens. — To begin with, it must be 
explained that there is a decided difference between a 
sample and a specimen of any material. A specimen is 
some of the material selected to show its prominent 
characteristics, either of an inferior or desirable nature. 
A sample, if properly taken, indicates the average com- 
position and character of the material it represents. 

Specimens are preferable to samples in certain instances 
and the reverse. When it is desired to emphasize the 
peculiarities of some material, a specimen is needed; but 
when a quantitative determination of its characteristics 
is to be made, a sample is necessary. 

This distinction must be borne in mind in selecting 
materials for examination, and good judgment must be 
used in regard to the most satisfactory means of arriving 
at the desired end. 

In preparation for the construction of an asphalt pave- 
ment the materials to be used should be carefully 
examined. 

Ordinarily the character of the rock which is to be 
used in the concrete and in the intermediate course, or 
surface, can be determined by mere inspection. The 
Portland cement will usually be examined and approved 
by the local authority and, in any case, the contractor 

141 



142 ASPHALT CONSTRUCTION 

will obtain it from the manufacturer under a guarantee 
that it complies with the local specifications. 

The materials which require careful inspection for use 
in the binder and the surface mixture of a sheet asphalt 
pavement include the sand, dust or filler, refined asphalt, 
and flux. After the work is under way the asphalt ce- 
ment as used and the surface mixture itself must be sub- 
jected to close control. 

Sand. — In order to select a proper supply of sand all 
of those which are locally available should be examined 
by screening and for this purpose 2 or 3 lb. should 
be sent to the laboratory tightly packed, so that no fine 
laterial can be lost, in a box of the size holding fifty 
cigars. Samples of the sand in use on the platform 
should be sent to the laboratory until it has been deter- 
mined that the grading is running satisfactorily. 

The sampling of sand must be carefully done in order 
to properly represent the material. The following direc- 
tions are taken from '^The Modern Asphalt Pavement." 

Sampling Sand. — First. From Pit or Bank. It must 
be borne in mind that in a pit or bank the sand lies in 
layers of different grading, which can almost never be 
taken out separately as a source of supply. Experience 
has shown that the best that can be done is to obtain a 
supply representing the average composition of the face 
of the bank. It is useless, therefore, to send specimens 
of sand from strata that cannot be isolated; or, if they 
are sent, specimens of the other layers in the bank should 
accompany them, with a statement of their relative thick- 
ness. A proper sample can be obtained by cutting a 
groove down the face of the bank and collecting the 
material in a pile and sampling as described below. 

Second. From Rivers or Lakeshores. In case it is 



INSTRUCTIONS FOR TAKING SAMPLES 143 

desired to sample sands from river bottoms or lakeshores, 
it is impossible in ordinary cases to send in more than 
what is considered to be a representative specimen of the 
material, and final sampling must await deliveries on 
scow or car. 

Third. Deliveries of sand should be sampled as follows : 
Small scoopsful or shovelsful are taken from different 
parts of the pile, car, or boatload, and at different depths, 
in such number as will fairly represent the lot, three to 
six, from a canal-boat or barge and at depths of a foot or 
more, two from a car, and more or less from a pile, de- 
pending on its size. When the sand is in a pile the coarser 
grains will have rolled to the bottom, so care must be 
exercised not to take the sand from that point or the top 
alone. It is also well to dig some distance into the heap 
for some scoopsful. 

All the sand thus collected is dried, and, if large in 
amount, is made into a heap, cut back and forth with 
shovels like a batch of concrete and quartered, all but 
one quarter being rejected. This is continued until the 
heap is reduced to such a size that it can be sampled by 
rolling first in one direction and then at right angles on 
I brown paper and halving the mass, this being done sev- 
eral times until it is reduced to the required size for 
shipping. 

Fourth. Sand from Platform. Samples of the hot 
I screened sand in use in the mixer should be taken from 
the spout of the sand-bin while the sand is running out 
I freely into the box in the process of filling it. It should 
)be collected by running a shovel or scoop back and 
iforth several times along the edge of the distributor 
land then sampling the lot so gathered by rolling on paper 

Idn the usual way. 
I 



144 ASPHALT CONSTRUCTION 

Dust and Filler. — The fine material proposed for use 
as a filler should be examined to determine the best 
source of supply available, and its character. An 
amount sufi&cient to fill an ordinary tin box used for 
asphalt cement is sufficient to send to the laboratory. 

Fluxes. — A tin can of the flux holding a pint should 
be sent to the laboratory for examination before using 
it, in order to determine its character and the amount 
necessary to make an asphalt cement of suitable 
consistency. 

Asphalt Cement. — Samples of asphalt cement should 
be examined for consistency either at the plant or at 
the control laboratory at frequent intervals, and also 
before being put in use, and at any time afterward that 
any additional amount of flux has been added to it to 
correct any hardening which has taken place. If the 
asphalt cement in any melting tank is not exhausted 
in one days run and is used the next day, or several 
days afterward, its consistency should be again con- 
trolled at the plant or at the control laboratory. 

Surface Mixtures. — Samples of surface mixtures 
should be taken for analysis daily, or oftener, for impor- 
tant work. The method of taking these samples is 
described as follows in ^^The Modern Asphalt Pavement": ' 

"Sampling Surface Mixture. — A small wooden paddle ' 
with a blade 3 to 4 in. wide, 5 or 6 in. long, and 1/2 in. thick, i 
tapered to an edge at one end and with a convenient handle ' 
at the other, is used to take as much of the hot mixture from ; 
the wagon as it will hold, being careful to avoid any of the ' 
last droppings from the mixer which may not be entirely I 
representative of the average mixture. Samples of mix- | 
ture should never be taken from the mixer itself, but only ' 
from the wagon after mixing is completed. 

"In the meantime a piece of brown Manila paper with : 
fairly smooth surface, 10 or 12 in. wide, and torn off at th( 



INSTRUCTIONS FOR TAKING SAMPLES 145 

same length from a roll of this paper, which can be had at 
any paper warehouse, is creased down the middle and opened 
out on some very firm and smooth surface of wood, not stone 
or metal, which would conduct heat too rapidly. The hot 
mixture is dropped into the paper sideways from the paddle 
and half of the paper doubled over on it. The mixture is 
then pressed down flat with a block of wood of convenient 
size until the surface is flat. It is then struck five or six 
sharp blows with the block, until the pat is about 1/2 in. 
thick. The paper should then be opened and the pat trimmed 
with an ordinary table knife or spatula to a size of about 
2 1/2 by 4 in., and a crease made along the narrower edge 
at a distance of 1/2 in. to facilitate breaking off a piece for 
analysis when the pat is cold. Before the mixture is entirely 
cold the proportions of sand, dust, arid asphalt cement, to- 
gether with the sample number, date, and abbreviation of the 
name of the city where the sample is taken, is impressed 
upon it with steel stamps in letters and figures 1/2 in. high. 
The paper is also marked with a rubber stamp, identifying it 
with the pat. 

'^Additional information as to street, kind of dust, asphalt, 
etc., can also be provided for in blank spaces opposite head- 
ings printed by the rubber stamp. Such a stamp may be 
arranged as follows: 

Name of city 

Sample number 

Date and hour 

Street 

Sand, coarse 

Sand, medium 

Sand,^ fine 

Filler* kind 

A. C... 

Asphalt, source 

Flux, kind 

Penetration A. C 

Temperature 

"The pat papers should be wrapped about the pat when 
cold and both placed in a heavy clasp envelope for mailing 
at parcel post rates. 

"The pat paper is sent because the stain made upon it 
by the asphalt of the hot mixture, when considered in con- 
nection with the temperature of the mixture as it goes on 

10 



146 ASPHALT CONSTRUCTION 

the street, is of great value in determining whether a suitable 
amount of bitumen is present. Nothing should be written 
on the pat paper, as this renders the entire pat liable to letter 
rates in mailing, but the information required may be sent 
by filling in the blanks furnished by the rubber stamp on a 
postal card and mailing this at the same time.'' 

Further detail in regard to the collection of samples 
is given in Chapter XVII of the book which has been 
cited. 



CHAPTER XVIII 
REFERENCE TABLES 

BEAUME, SPECIFIC GRAVITY AND POUNDS PER GALLON AT 

60° F. 



Beaume 


Specific 


Lbs. in Specific 


i 
Lbs. in 


Beaume 




gravity 


U. S. gal. gravity 


1 U. S. gaL 




10. 


1. 000 


S.33 I 


.000 


S.33 


10. 


II. 




.993 


8 


.27 


.995 


8.29 


10.7 


12.0 




.986 


8 


. 21 


.990 


8.25 


II. 4 


130 




.979 


8 


.16 


.985 


8.21 


12. 1 


14.0 




.973 


8 


. 10 


.980 


8.16 


12.9 


15.0 




.966 


8 


.05 


.975 


8.12 


13.6 


16.0 




•959 
.953 


7 
7 


.99 _ 


.970 
.965 


8.08 
8.04 


14.3 


17.0 


94 


15. 1 


18.0 




.947 


7 


88 


960 


8.00 


15.9 


19.0 




.940 


7 


S3 


955 


7:96 


16.6 


20.0 




.934 


7 


78 


950 


7.91 


17-4 


21.0 




928 


7 


73 


945 


7^^? 


18.2 


22.0 




922 


7 


68 


940 


7-S3 


19.0 


23.0 




916 


7 


63 


935 


7.79 


19.8 


24.0 




910 


7 


58 


930 


7-75 


20.6 


25.0 




904 


7 


53 


925 


7-7^ 


21.4 


26.0 




898 


7 


48 


920 


7.66 


22.3 


27.0 




893 


7 


44 


915 


7.62 


23.1 


28.0 




887 


7 


39 


910 


7.58 


24.0 


29.0 




882 


7. 


34 


905 


7.54 


24.8 


30.0 




876 


7- 


30 


900 


7.50 


25.7 


31.0 




871 


7. 


25 


895 


7.46 


26.6 


32.0 




S65 


7. 


21 


890 


7.41 


27.4 


33-0 




860 


7. 


17 


8Ss 


7^37 


28.3 


34.0 




855 


7- 


12 


880 


7-33 


29-3 


35.0 




850 


7- 


08 


875 


7.29 


30.2 


36.0 




845 


7. 


04 


870 


7-25 


31. 1 



147 





TEMPERATURES, CENTIGRADE AND FAHRENHEIT 


c. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


c. 


F. 


o 





























-29 


— 20.2 


17 


62.6 


63 


14s. 4 


109 


228.2 


155 


311. 


28 


18.4 


18 


64.4 


64 


147.2 


no 


230.0 


IS6 


312.8 


27 


16.6 


19 


66.2 


6S 


149.0 


III 


231.8 


IS7 


314.6 


' 26 


14.8 


20 


68.0 


66 


ISO. 8 


112 


233.6 


IS8 


316.4 


25 


13.0 


21 


69.8 


67 


IS2.6 


113 


23s. 4 


IS9 


318.2 


24 


II. 2 


22 


71.6 


68 


IS4.4 


114 


237.2 


160 


320.0 


23 


9.4 


23 


73.4 


69 


IS6.2 


115 


239.0 


161 


321.8 


22 


7.6 


24 


7S-2 


70 


1S8.0 


116 


240.8 


162 


323.6 


21 


S.8 


2S 


77.0 


71 


IS9.8 


117 


242.6 


163 


325.4 


20 


4.0 


26 


78.8 


72 


161. 6 


118 


244.4 


164 


327.2 


19 


2.2 


27 


80.6 


73 


163.4 


119 


246.2 


I6S 


329.0 


18 


0.4 


28 


82.4 


74 


16S.2 


120 


248.0 


166 


330.8 


17 


+ 1.4 


29 


84.2 


7S 


167.0 


121 


249.8 


167 


332.6 


16 


3.2 


30 


86.0 


76 


168.8 


122 


251.6 


168 


334.4 


IS 


S.o 


31 


87.8 


77 


170.6 


123 


253.4 


169 


336.2 


14 


6.8 


32 


89.6 


78 


172.4 


124 


2SS.2 


170 


338.0 


13 


8.6 


33 


91.4 


79 


174.2 


125 


257.0 


171 


339.8 


12 


10.4 


34 


93.2 


80 


176.0 


126 


258.8 


172 


341.6 


II 


12.2 


3S 


9S.0 


81 


177.8 


127 


260.6 


173 


343.4 


10 


14.0 


36 


96.8 


82 


179.6 


128 


262.4 


174 


34S.2 


9 


IS. 8 


37 


98.6 


83 


181. 4 


129 


264.2 


+ I7S 


+347.0 


8 


17.6 


38 


100,4 


84 


183.2 


130 


266.0 


176 


348.8 


7 


19.4 


+ 39 


+ 102.2 


8S 


185.0 


131 


267.8 


177 


3S0.6 


6 


21.2 


40 


104.0 


86 


186.8 


132 


269.6 


178 


3S2.4 


5 


23.0 


41 


1OS.8 


87 


188.6 


133 


271.4 


179 


3S4.2 


4 


24.8 


42 


107.6 


88 


190.4 


134 


273.2 


180 


3S6.0 


3 


26.6 


43 


109.4 


89 


192.2 


I3S 


275.0 


181 


3S7.8 


2 


28.4 


44 


III. 2 


90 


194.0 


• 136 


276.8 


182 


3S9.6 


I 


30.2 


4S 


I130 


91 


195.8 


137 


278.6 


183 


361.4 





32.0 


46 


114. 8 


92 


197.6 


138 


280.4 


184 


363.2 


+ 1 


33.8 


47 


116. 6 


93 


199.4 


139 


282.2 


185 


365.0 


2 


3S.6 


48 


118. 4 


94 


201.2 


140 


284.0 


186 


366.8 


3 


37.4 


49 


120.2 


9S 


203.0 


141 


285.8 


187 


368.6 


4 


39.2 


SO 


122.0 


96 


204.8 


142 


287.6 


188 


370.4 


5 


41.0 


SI 


123.8 


97 


206.6 


143 


289.4 


189 


372.2 


6 


42.8 


S2 


125.6 


98 


208.4 


144 


291.2 


190 


374.0 


7 


44.6 


S3 


127-4 


99 


210.2 


14s 


293.0 


191 


375.8 


8 


46.4 


S4 


129.2 


100 


212.0 


146 


294.8 


192 


377.6 , 


9 


48.2 


ss 


131.0 


lOI 


213.8 


147 


296.6 


193 


379.4 


10 


So.o 


S6 


132.8 


102 


215.6 


148 


298.4 


194 


381.2 


II 


SI. 8 


S7 


134.6 


103 


217.4 


149 


300.2 


195 


383.0 : 


12 


S3. 6 


S8 


136.4 


104 


219.2 


ISO 


302.0 


196 


384.8 


13 


SS.4 


S9 


138.2 


los 


221.0 


iSi 


303.8 


197 


386.6 


14 


S7.2 


60 


140.0 


106 


222.4 


IS2 


305.6 


198 


388.4 1 


IS 


S9.0 


61 


141. 8 


+ 107 


+ 224.6 


IS3 


307.4 


199 


390.2 


16 


60.8 


62 


143.6 


108 


226.4 


IS4 


309.2 


200 


392.0 j 



148 



INSTRUCTIONS FOR TAKING SAMPLES 149 
TEMPERATURES, CENTIGRADE AND FAURENUEIT.— {Continued) 



c. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


o 


o 


























201 


393.8 


223 


433.4 


24s 


473.0 


267 


512.6 


289 


552.2 


202 


395.6 


224 


435.2 


246 


474.8 


268 


514.4 


290 


554.0 


203 


397.4 


225 


437.0 


247 


476.6 


269 


516.2 


300 


572.0 


204 


399.2 


226 


438.8 


248 


478.4 


270 


518.0 


310 


590.0 


205 


401.0 


227 


440.6 


249 


480.2 


271 


519.8 


320 


608.0 


206 


402.8 


228 


442.4 


250 


482.0 


272 


521. 6 


330 


626.0 


207 


404.6 


229 


444.2 


251 


483.8 


273 


523.4 


340 


644.0 


208 


406.4 


230 


446.0 


252 


485.6 


274 


525.2 


350 


662.0 


209 


408.2 


231 


447.8 


253 


487.4 


275 


527.0 


360 


680.0 


210 


410.0 


232 


449.6 


254 


489.2 


276 


528.8 


370 


698.0 


211 


411. 8 


233 


451.4 


255 


491.0 


277 


530.6 


380 


716.0 


212 


413.6 


234 


453.2 


256 


492.8 


278 


532.4 


390 


734.0 


213 


415.4 


235 


455.0 


257 


494.6 


279 


534.2 


400 


752.0 


214 


417.2 


236 


456.8 


258 


496.4 


280 


536.0 


410 


770.0 


215 


419.0 


237 


458.6 


259 


498.2 


281 


537.8 


420 


788.0 


2l6 


420.8 


238 


460.4 


260 


500.0 


282 


539.6 


430 


806.0 


217 


422.6 


239 


462.2 


261 


- 501.8 


283 


541.4 


440 


824.0 


2l8 


424.4 


240 


464.0 


262 


503.6 


284 


543.2 


450 


842.0 


219 


426.2 


241 


465.8 


263 


505.4 


285 


545.0 


460 


860.0 


220 


428.0 


242 


467.6 


264 


507.2 


286 


546.8 


470 


878.0 


221 


429.8 


+ 243 


+469.4 


265 


509.0 


287 


548.6 


480 


896.0 


222 


431.6 


' 244 


471.2 


266 


510.8 


288 


550.4 


490 
500 


914.0 
932.0 



DATA, ROCK 





Special 
gravity 


Weight per 
cu. ft. lb. 


Weight per cu. yd. 
broken stone 


Rock 


48 

per cent. 

voids 


40 

per cent. 

voids 


Trao 


2.90 
3.00 
2.65 


181 
187 
165 


2538 
2619 
2316 


2932 
3029 
2617 


Trap and Gabbro . . . 
Limestone and Gran- 
ite 







150 ASPHALT CONSTRUCTION 

Concrete 

I barrel of Portland cement, or four bags, will lay, 
ordinarily, 6 sq. yd. of i : 3 : 6 concrete. 

Binder or Intermediate Course 

9 cu. ft. of loose hot binder will lay 6.6 sq. yd. of 1.5- 
in. intermediate course. 

Sheet Asphalt Surface 

9 cu. ft. of loose hot surface mixture will lay 5.1 sq. 
yd. of 2-in. pavement. 



I 



INDEX 

A 

Page 

Advice to engineers, contractors and inspectors 121 

Aggregates containing fine stone 33 

Asphalt, Bermudez 4i> 46 

composition of refined 47 

block mixtures, examination of 137 

blocks, composition of, 33? 90 

broken stone surfaces 99 

cement 52 

penetration of 134 

fluxing 52 

macadam 99 

Trinidad 41 

Lake, composition of, 45 

refined, analysis of 46 

Asphaltic broken stone highways 24, 99 

concrete 24, 113 

broken stone for 6. 98 

mixtures, examination of 137 

^ surface. Long Island City 96 

^ Muskegon, Mich 97 

surfaces 95 

Asphalts. 39 

B 

Beaume, degree, equivalent specific gravity 149 

Bermudez asphalt 41, 46 

composition of refined 57 

Binder 116 

asphaltic road 100 

close 19 

open 16 

stone 6 

151 



152 INDEX 

Page 

Bitumens, native 39 

Bituminous broken stone surfaces 99 

Blocks, asphalt, composition of $z, 90 

examination of 137 

Broken stone 5 

for asphaltic concrete 98 

weight per cubic yard 149 

C 

Carpet coats 103 

Cement, asphalt 52 

Citizens, suggestions to. 125 

Concrete, asphaltic 22, 113 

as foundation 9 

gravel in 11 

segregation of 10 

surfaces 95 

Contractors, suggestions to 123 

Crushers, for broken stone S 

Crusher, run of 6 

D 

Density, sheet asphalt surface 79 

Distributors, mechanical loi 

Dust 35 

E 

Engineers, suggestions to 121 

F 

Fifth Avenue pavement, New York 64 

Filler 35 

Flow test 135 

Fluxes 48 

Foundation 8 

Foundations, other than concrete 12 



INDEX 153 

G 

Page 

Gallons, weight per i47 

Gravel, in concrete ii 

Grit mixtures 9° 

H 

Heaters, surface no 

I 

Impact tests of sheet asphalt surface 80 

Inspectors, suggestions to 124 

Instructions, Circular of 1896 69 

H. B. PuUar 85 

for taking samples 141 

[ntermediate course 16 

L 

Laboratory 7 127 

Limestone 6 

London, pavement on Kings Road, Fulham 61 

on Victoria Embankment 43? 63 

i 

I M 

Macadam, asphalt 99 

as foundation 13 

Maintenance and repairs 107 

Melting tanks 100, 114 

Methods of examination 130 

Mineral aggregate 25 

examination of 135 

I Mixers 114 

I Mixtures, grit 90 

sheet asphalt 56 

surface 56 

j asphalt, 191 2 66 

' Topeka 90, 93 

unsatisfactory 75 



154 INDEX 

N 

Page 

New York, Fifth Avenue pavement 64 

sheet asphalt mixtures in 1912 66 

P 

Paris, Avenue Victoria pavement 67 

Pat paper test 74 

Pavement, Fifth Avenue, New York 64 

Kings Road, Fulham, London 61 

Paris, Avenue Victoria 67 

Vermont Avenue, Washington, D. C 26, 42 

Victoria Embankment, London 43-63 

Penetration of asphalt cement 134 

Plant 112 

R 

Repairs 107 

Residuums 48 

Road binder, asphaltic 100 

Rock, specific gravity, weight of 149 

S 

Sand 25 

sampling of 142 

Sands, standard grading 29 

Screening of mineral aggregate 135 

of surface mixtures 135 

Sheet asphalt mixtures 56 

unsatisfactory 75 

surfaces 25 

action of water on 81 

density of 79 

impact test of 80, 82, 83 

Sieves 26 

Specific gravity, equivalent degree, Beaume 147 

Stone, asphaltic broken, surfaces 99 

binder 6 



INDEX 155 

Page 

broken 5 

weight per cubic yard 149 

Street, work upon 117 

Suggestions to citizens 125 

to contractors 123 

to engineers 121 

to inspectors 124 

Surface heaters no 

mixtures 56 

Surfaces, asphaltic concrete 95 

Long Island City, 1896 96 

Muskegon, Mich 97 

bituminous broken stone 99 

Evans, tar, Washington, 1873 9^ 

T 

Tanks, melting 100, 114 

Test flow 135 

pat paper 74 

Thames Embankment {see Victoria Embankment) 43-63 

Thermometers, Centigrade and Fahrenheit equivalents 148 

Topeka mixture QOj 93 

Trap rock 6 

Trinidad asphalt pavement, Vermont Avenue, Washington, 

D. C 26-42 

lake asphalt, composition of 45 

refined, analysis of 46 

V 

Vermont Avenue pavement, Washington, D. C 26, 42 

Victoria Embankment pavement, London 43; 63 

W 

Washington, pavement on Vermont Avenue 26, 42 

Water, action of, on sheet asphalt 81 

Work upon the street 117 



APR 25 1SI3 



